A good workshop starts on a good foundation, or in my case a temporary cinder block footers foundation. I did not want a permanent foundation so I used cinder blocks footers to support the pressure treated 2×6 floor joists that I used. I laid them 16” O.C. and then insulated them with R19 fiberglass insulation. Then I used 3/4” tongue and groove OSB for the sub-floor, I screwed down the OSB so the floor doesn’t squeak. In the end, it came out level, square, and very sturdy.
Thanks for looking.