Exhibit 99.3

UNAUDITED PRO FORMA CONDENSED COMBINED FINANCIAL INFORMATION

The following unaudited pro forma condensed combined financial statements present the combination of the historical financial statements of Beacon and Allied, adjusted to give effect to the Allied Transactions. As used herein, the term “Allied Transactions” refers to the following proposed transactions: (i) a $300.0 million public offering of shares of Beacon’s common stock; (ii) the Debt Financing (as defined herein); (iii) the Convertible Preferred Stock Purchase (as defined herein); (iv) the closing of the Allied Acquisition (as defined herein); (v) the repayment of certain existing indebtedness of Beacon; and (vi) the payment of estimated premiums, fees and expenses in connection with the proposed $300.0 million public offering of shares of Beacon’s common stock, the proposed Debt Financing, the Allied Acquisition and the Convertible Preferred Stock Purchase.

The unaudited pro forma condensed combined balance sheet information gives effect to the Allied Transactions as if they had been consummated on June 30, 2017 and includes pro forma adjustments based on Beacon management’s preliminary valuations of certain acquired tangible and intangible assets. Beacon’s fiscal year ends on September 30, while Allied’s last three fiscal years ended on December 31, 2016, January 2, 2016 and December 27, 2014. The unaudited pro forma condensed combined statement of operations information for the fiscal year ended September 30, 2016 gives effect to the Allied Transactions as if they had been consummated on October 1, 2015 and combines Beacon’s historical results for the fiscal year ended September 30, 2016 with Allied’s historical results for the fiscal year ended December 31, 2016. As Allied’s fiscal year end is within 93 days of Beacon’s fiscal year end, the unaudited pro forma condensed combined statement of operations information for the fiscal year ended September 30, 2016 includes Allied’s annual operating results for its respective fiscal year ended December 31, 2016. The unaudited pro forma condensed combined statement of operations information for the nine months ended June 30, 2017 gives effect to the Allied Transactions as if they had been consummated on October 1, 2016 and combines Beacon’s historical results for the nine months ended June 30, 2017 with Allied’s historical results for the six months ended July 1, 2017 and the three months ended December 31, 2016.

The final terms of the Allied Transactions, including the Debt Financing, will be subject to market conditions and may change materially from the assumptions described in the following unaudited pro forma condensed combined financial statements. Changes in assumptions with respect to the Allied Transactions would result in changes to various components of the unaudited pro forma condensed combined balance sheet, including stockholders’ equity and total debt, and various components of the unaudited pro forma condensed combined statements of operations, including interest expense and earnings per share. Depending on the nature of the changes, the impact on the unaudited pro forma condensed combined financial information could be material.

The unaudited pro forma condensed combined financial statements were prepared using the acquisition method of accounting for business combinations under the guidance of Accounting Standards Codification Topic 805, Business Combinations (“ASC 805”). Under ASC 805, assets acquired and liabilities assumed are recorded at fair value, with any excess purchase price allocated to goodwill.    The fair value of identifiable tangible and intangible assets acquired and liabilities assumed are preliminary and are based upon available information and certain assumptions described in the accompanying notes to the unaudited pro forma condensed combined financial statements that Beacon’s management believes are reasonable under the circumstances. The final purchase price allocation for the Allied Transactions will be performed after the closing of the Allied Acquisition and will depend on the actual net tangible and intangible assets that exist as of the closing of the Allied Acquisition. Any final adjustments may change the allocation of purchase price, which could result in a change to the unaudited pro forma condensed combined financial information, including goodwill. The result of the final purchase price allocation could be materially different from the preliminary allocation set forth herein.

The unaudited pro forma condensed combined financial information is provided for informational and illustrative purposes only and is not intended to represent or be indicative of the consolidated results of operations or financial position of Beacon that would have been reported had the Allied Transactions been completed as of the dates presented, and should not be taken as representative of the future consolidated results of operations or financial position of Beacon following the consummation of the Allied Transactions. We therefore caution you not to place undue reliance on the unaudited pro forma condensed combined financial information. The unaudited pro forma condensed combined financial information should be read in conjunction with:

Beacon Roofing Supply, Inc.

Unaudited Pro Forma Condensed Combined Statements of Operations

For the Nine Months Ended June 30, 2017

Beacon Roofing Supply, Inc.

Unaudited Pro Forma Condensed Combined Statements of Operations

For the Fiscal Year Ended September 30, 2016

Beacon Roofing Supply, Inc.

Unaudited Pro Forma Condensed Combined Balance Sheet

As of June 30, 2017

Notes to Unaudited Pro Forma Condensed Combined Financial Information

On August 24, 2017, Beacon entered into a stock purchase agreement (the “Stock Purchase Agreement”) with Oldcastle, Inc. and Oldcastle Distribution, Inc., pursuant to which Beacon will acquire for approximately $2.625 billion in cash (subject to a working capital and certain other adjustments as set forth in the Stock Purchase Agreement) (the “Purchase Price”) all of the issued and outstanding shares of capital stock of Allied Building Products Corp. and an affiliated entity (together with its and their respective subsidiaries, “Allied”), on the terms and subject to the conditions set forth in the Stock Purchase Agreement (the “Allied Acquisition”).

To finance this transaction, Beacon has entered into a commitment letter with lenders for the following debt financing facilities:

In connection with the aforementioned debt financing (the “Debt Financing”), Beacon plans to enter into the following equity financing transactions to further finance the Allied Acquisition:

The unaudited pro forma condensed combined financial information has been prepared pursuant to the rules and regulations of the SEC. Certain information and certain footnote disclosures normally included in financial statements prepared in accordance with U.S. generally accepted accounting principles have been condensed or omitted pursuant to such rules and regulations.

The unaudited pro forma condensed combined balance sheet information gives effect to the Allied Transactions as if they had been consummated on June 30, 2017 and includes pro forma adjustments based on Beacon management’s preliminary valuations of certain tangible and intangible assets. Beacon’s fiscal year ends on September 30, while Allied’s last three fiscal years ended on December 31, 2016, January 2, 2016 and December 27, 2014. The unaudited pro forma condensed combined statement of operations information for the fiscal year ended September 30, 2016 gives effect to the Allied Transactions as if they had been consummated on October 1, 2015 and combines Beacon’s historical results for the fiscal year ended September 30, 2016 with Allied’s historical results for the fiscal year ended December 31, 2016. As Allied’s fiscal year end is within 93 days of Beacon’s fiscal year end, the unaudited pro forma condensed combined statement of operations information for the fiscal year ended September 30, 2016 includes Allied’s annual operating results for its respective fiscal year ended December 31, 2016. The unaudited pro forma condensed combined statement of operations information for the nine months ended June 30, 2017 gives effect to the Allied Transactions as if they had been consummated on October 1, 2016 and combines Beacon’s historical results for the nine months ended June 30, 2017 with Allied’s historical results for the six months ended July 1, 2017 and the three months ended December 31, 2016.

The unaudited pro forma condensed combined financial statements were prepared using the acquisition method of accounting for business combinations under the guidance of Accounting Standards Codification Topic 805, Business Combinations (“ASC 805”). Under ASC 805, assets acquired and liabilities assumed are recorded at fair value, with any excess purchase price allocated to goodwill. The fair value of identifiable tangible and intangible assets acquired and liabilities assumed are preliminary and are based upon available information and certain assumptions described in the accompanying notes to the unaudited pro forma condensed combined financial statements that Beacon’s management believes are reasonable under the circumstances. The

final purchase price allocation for the Allied Transactions will be performed after the closing of the Allied Acquisition and will depend on the actual net tangible and intangible assets that exist as of the closing of the Allied Acquisition. Any final adjustments may change the allocation of purchase price, which could result in a change to the unaudited pro forma condensed combined financial information, including goodwill. The result of the final purchase price allocation could be materially different from the preliminary allocation set forth herein.

Following the Allied Acquisition, Beacon will conduct a review of accounting policies of Allied in an effort to determine if differences in accounting policies require reclassification of results of operations or reclassification of assets or liabilities to conform to Beacon’s accounting policies and classifications. As a result of that review, Beacon may identify differences among the accounting policies of the companies that, when conformed, could have a material impact on the unaudited pro forma combined financial information.

Definite lived intangible assets consisting of amounts assigned to customer relationships are expected to be amortized over their estimated life of 20 years on an accelerated basis. Estimated future amortization for the five year period following the closing date of the Allied Acquisition is $86.8 million, $122.5 million, $108.3 million, $91.8 million, and $75.5 million for the years ending September 30, 2017, 2018, 2019, 2020, and 2021, respectively.

Beacon estimates the weighted-average interest rate on the new indebtedness to be approximately 4.6%. A hypothetical 1/8 percent increase or decrease in the expected weighted-average interest rate, including from an increase in LIBOR, would increase or decrease interest expense on Beacon’s financing by approximately $35.8 million annually.

For purposes of the unaudited pro forma condensed combined statement of operations, the combined United States federal and state statutory tax rate of 39.0% has been used for all periods presented. This does not reflect Beacon’s effective tax rate, which includes other tax items such as tax charges or benefits, and does not take into account any historical or possible future tax events that may impact Beacon in the future.

Assuming a full conversion of the preferred stock outstanding at the beginning of the period (see Note 4(d)), the pro forma adjustment to diluted weighted-average common stock outstanding for the nine months ended June 30, 2017 and year ended September 30, 2016 would be increases of approximately 14.6 million shares and 14.7 million shares, respectively.

Assuming no conversion of preferred stock in the period and an assumed 6% annual dividend on the convertible preferred shares outstanding, the following represents the calculation of the pro forma adjustment to net income per share for the respective periods presented (in thousands, except share and per share amounts):

Assuming full conversion of preferred stock at the beginning of the period, the following would represent the calculation of the pro forma adjustment to net income per share for the respective periods presented (in thousands, except share and per share amounts):

Below is a preliminary allocation of the total purchase price and the pro forma adjustments to the unaudited pro forma condensed combined balance sheet as of June 30, 2017 (in thousands):

The adjustments to the historical combined net assets as a result of the allocation of the estimated purchase price for Allied are as follows (in thousands):

Upon completion of the fair value assessment, the Company anticipates that the final purchase price allocation will differ from the preliminary assessment provided above. Any changes to the initial estimates of the fair value of the assets and liabilities will be recorded as adjustments and the residual amounts will be allocated as an increase or decrease to goodwill.

Deferred financing fees of approximately $52.0 million have been recorded against the gross long-term debt balances. Deferred financing fees will be amortized over the contractual term of the respective facilities. Deferred financing fees of $13.8 million relating to Beacon’s existing long-term debt have been eliminated from total assets with a corresponding decrease to retained earnings for the amounts related to Beacon. No adjustment has been made to the unaudited pro forma combined statements of operations for these costs, as they are non-recurring.