Cameron, I just put a floor in my 20x20 shop and floated the floor because I was afraid if I fastend it into the slab it would be my luck it would leak.
I put 2 rows of 2x4s down the middle and put 1 row of 2x4s on each wall. These got north-south. The added 2x4s across (east-west) every 24 inches. I used hard foam insultation between the 2x4s since I'm trying to keep the cold out. On top I put 3/4 OSB T&G.
I just toe nailed the 2x4s into the sill plate around the perimiter. If I ever move I can just unscrew everything.
One thing I should have done was used 3/4 1 sided sanded plywood instead of OSB. It would have looked nicer. I painted the floor but I have pulled up flakes here and there. Its a shop so I really don't care.
Don