Builders FirstSource IncDOW SkillBridge Military Application (Iowa) Builders FirstSource IncDOW SkillBridge Military Application (Iowa)Sioux City, IAIgnite your career at Builders FirstSource, America's largest supplier of building materials, value-added components and building services to the professional market. At BFS, you'll be equipped with all the tools, training, and resources you need, and you'll be empowered to try new things, gain new experiences, and build a career with unlimited horizons.