Whenever I do frame work, I never consider the floor. I either make a level surface or level the frame by bubble. Most of the time, that includes setting jack stands at the same height, then shimming between the frame and the jack stand where necessary. Way back when, I put the Suburban on jack stands. My current project, the Model A, is on a level frame building jig. Which actually works out better as you don't having to worry about kicking jack stands around or knocking shims off, even though they are taped in place.
