Builders FirstSource supplies the materials that become American houses: lumber, engineered wood, roof trusses, wall panels, windows, doors and millwork. Homebuilders are the main customers, and the company increasingly sells manufactured components rather than raw boards, moving labor from the jobsite into its factories. Built through a long string of acquisitions across a fragmented industry, it is the largest supplier of its kind in the United States. Results track housing starts, making the stock a leveraged play on residential construction.