I can go either way.  But what about construction cost each way?  Concrete slab total cost for 32’x40′ is $8320 ($6.50 / sq ft quote for post tensioning).  Probably 1/3 of that for footings alone.  Plus another 1/3 for concrete block stem wall.  Then add framing for sub-floor.  Looks like it would be about the same cost either way. 

Would one concrete block above grade and two below, all setting on a 18″x18″ footing be sufficient?  (max frost line is about 2′)   Dig out interior to level of top of footing.  That would give a 24″ crawl space under.

How often would 2×8 floor joists need support?  I figure 10′ would be fine.

What about decking?  My inlaws house used 2×8 SYP (1950 vintage), asphalt felt paper, then oak floors.

And, lastly, what are the advantages/disadvantages for either type of floor?