I know my dad recently built a shop that is 24'x36' and the crew that built it for him made it from 4x6 posts with 2x6 "beams" running horizontal. He had that built, with a monolithic pour of concrete, metal siding and metal roof, insulated, and 1/2" plywood on all walls, with (2) 9'x8' doors, (1) walk in door, and (2) smaller windows. He only paid $10,000, but he had the base already in place. He had a bunch of cinder gravel poured in the back yard about 4 years before he built the garage. He just parked in different spots over the years to pack down the gravel. Hasn't had any problems with it yet. He wired it all himself though, so that wasn't included in the price.