Steel building envelope (26-29 gauge metal panels) with residential fit-out. Advantages: fast erection (shell in days), large open spans (60-100 ft clear), low maintenance exterior, pest resistant. Interior: conventional framing, insulation, drywall, plumbing, HVAC. Code challenge: may require commercial occupancy classification depending on jurisdiction. Spray foam insulation for condensation control. Cost: $100-$250/sf (significantly less than conventional). Growing: Texas, Oklahoma, Southeast.