My garage built on a side hill has two floors. From the front of the garage, it looks like a single story garage with triple garage doors. But this is really the second floor. The garage floor is a special concrete mix using pea gravel approximently three and a half inches thick. This was poured directly on a 3/4" T&G subfloor built over engineered floor joists 12" OC. (lots and lots of rebar over thick poly film, also) Although I chose to simply smooth finish the floor, any finish could have been applied, including stamped, acid etched/ stained finishes. The floor has been in place nearly six years and, so far, so good.
Good luck.
Kep