I've moved into a place that has a large (24 x 50) pole barn on the property. I've started the process of converting it into an enclosed building and I intend to set up my shop in it. I have discovered that the existing concrete slab is not at all flat and is out of level by about 2 inches over a span of about 20 feet.
My previous shop was in a basement, also on concrete slab, also out of level and not flat. It was a nuisance having to fiddle with roller stands and other temporary supports to compensate for it as was necessary when I moved them. Other than that, I never really noticed the flaw in the floor.
I'm considering putting a plywood floor on top of the slab anyway, just so I don't have to stand on concrete. Would it be worth the trouble to raise that floor on sleepers and shim them so the floor is level? Can such a structure be made stiff enough to work well under heavy machinery?
----------------------------------------------------------------------------------- Yes, you can make it stiff enough for machines, by supporting the floor joists often by putting shims down against the concrete along the length.
The largest advantage of putting down a wood floor, is the opportunity to put wire runs down in the floor. I would put a section of plywood down with screws, so you can remodel the wires in the future.
Also, dust collection in the floor is like sliced bread. No ducts coming down from the ceiling to get in the way of long pieces of wood or plywood. Once again, even if you don't put it down now, build for putting ducts in, sometime in the future.
This is a bit of money to spend, but the payoff could be great. Go for it if you can.
If you want to do the ducts, I would use 2 x 6 joists, shimmed with 2x4's at the minimum so a 8 inch duct will fit. Go with 12' O.C. spacing and support them on the floor about every 4 or 6 feet.
-- Jim in NC