If working with stone; what I like to do is sink it partially into the ground by building the first piece on a bit of ground that is just slightly lower in elevation, so I've got some leeway with imperfections on what's supposed to be a flat ground. With wood floors, I prefer the option where the floor is about 0.5m above the ground and supported by 1m wood beams. (higher, and 1m supports might not be enough in some places, lower and it gets very hard to place the supports)
(also, when leveling terrain, stand on a bit of terrain that you want the other terrain to match in height to)

Beyond making sure the ground floor is all even, frame+roof is what I do next, and then everything else will fall into place and should be supported.