I wanted a concrete slab in mine. My builder dug a trench around the perimeter 3+' deep x 18" wide, no forms. They just poured the trench until it was full, and went around and stuck rebar in every 2' going straight down all the way around, and left for the day. Next morning using pipes to act as levers they bent the rebar over into the area where the pad would be. Laid a fibermat that I guess is used in commercial concrete pours, instead of a rebar grid. Builder said it was way more cost than rebar, but did a much better job of holding it all together, and was way less time intensive, so overall a much better job, for about the same cost when Man hours were figured in. Then they pour the slab over the wall already there, and out into the field. Called it a "Unipour," all I know is the county guy was walking around shaking his head, and smiling a lot. They did put up a form for the pad pour, but it was pretty rudimentry, just to stop the lop from running over. County guy said he'd never seen "one of these" on anything less than 4 stories tall, he was all happy to approve it. That and the fact the pad when dried was exactly 32' x 48' the dead exact size of the barn/garage, and they bolted, rather than strapped the sill plates down to the pad. I was pretty happy with the pour, and now after 4 years there are only the expansion cracks, no other breaks, even small ones on the floor.
Worst thing they can do is cook ya and eat ya 
GW
GW