X0306 4 2021-01-01 0 0001316835 Builders FirstSource, Inc. BLDR 0001212607 ALEXANDER MARK A C/O BUILDERS FIRSTSOURCE, INC. 2001 BRYAN ST., SUITE 1600 DALLAS TX 75201 1 0 0 0 Common Stock, par value $0.01 per share 2021-01-01 4 A 0 25707 A 25707 D Received in exchange for 13,974 shares of BMC Stock Holdings, Inc. ("BMC") common stock, par value $0.01 per share, and 5,613 restricted stock units of BMC in connection with the completion of the merger (the "Merger"), on January 1, 2021 (the "Effective Date"), of Boston Merger Sub I Inc., a subsidiary of the Issuer, with and into BMC, pursuant to the Agreement and Plan of Merger, dated as of August 26, 2020 (the "Merger Agreement"). On the Effective Date, each outstanding BMC restricted stock unit vested and settled into 1.3125 shares of the Issuer's common stock, par value $0.01 per share, and each share of BMC common stock was converted automatically into the right to receive 1.3125 shares of the Issuer's common stock, par value $0.01 per share, in each case, in accordance with the Merger Agreement. /s/ Minator Azemi, by power of attorney 2021-01-05