Hi. I have an eight hundred square ft. shop 21/2" out of level and a rough concrete floor (left as if they raked it and when to the bar). It has 8ft head room. Some say to pour another 4" concrete on it while others say jack it up and put a engineered truss floor under the shop and others say shim in 2x4 floor joists @ 12" spacing and cover with 3/4" ply and some kind of flooring on top. I want to set up a wood workin g shop. Help I can't figure out what is best. Hope you can help. Thanks in advance. Ed Bettiss.