If you know where you hoist is going, have your concrete contractor use rebar around that area for added strength. This will help to insure it won't crack around those areas. Also before the slab is poured, rent a plate tamper for a few hours and go around the perimeter and in the corners to firm up the gravel fill. Usually a garage is just filled with gravel and the slab poured on top. After a few years the gravel will settle and leave voids underneath. You can always tell in someones garage by walking around and thumping the floor with something like a spud bar. And it seems the corners will settle and water always wants to puddle there. Make sure the concrete is sloping away from the walls. Looking forward to more pics. Be sure to post.
Kevin