I had a 2nd garage built, 24' x 30', similar to this: steel roof and siding. It was built by a 3-5 man crew, taking a couple of weeks: site preparation (BobCat), removing 18" of soil, leveling sand atop that; anchoring 6x6 vertical wall posts; concrete driveway and floor, with a floor drain out the side; insulation on the walls (see below).
To say that he built that in, "one day," is very misleading advertising. LOL!
I had two different inspectors look at my garage, due to the builder not following the blueprints to the letter: he used a slightly different bolt than what was called for in the blueprints, to secure the roof rafters, so he had to switch them out -- both met code, but the first did not match what the blueprints specified, and they held him to
exactly what was listed on the blueprints, no matter what. Second inspector commented it was built like a bunker (6x6 vertical wall posts).
Still need to put sheet metal, or plywood, across the ceiling, then insulate it... Builder never mentioned that I was only buying
wall insulation -- ceiling insulation was not included.
Caveat Emptor! 
Cheers!