On metal, spray foam is best way..... But as far as walls, it all depends on the construction of the metal building. I had a 30x30 that was red metal beam. While quick and great strength with the beams, the beam's internal angle made it impossible to really do inner wall well. This angle, along with the raised base panel made me go with separate internal wall where I wanted to enclose the area. I'd never build another that I expected to need to use the internal walls for storage. If straight vertical walls with straight horizontal beams, then I'd do the minimum right now. Things are coming down, but not fast. Sheetrock is actually not a bad idea, but if you are attaching a lot of heavy stuff, maybe a slat wall would be best.
Woodworking, Old Tools and Shooting
Ray Fine RF-1390 Laser Ray Fine 20watt Fiber Laser
SFX 50 Watt Fiber Laser
PM2000, Delta BS, Delta sander, Powermatic 50 jointer,
Powermatic 100-12 planer, Rockwell 15-126 radial drill press
Rockwell 46-450 lathe, and 2 Walker Turner RA1100 radial saws
Jet JWS18, bandsaw Carbide Create CNC, RIA 22TCM 1911s and others