Questions about enclosing a carport

I have a 4 bay gravel floor carport behind my garage.  The corner posts are 8x8 set in concrete and intermediate posts are 6x6 set in concrete.  The top is a foot thick steel box section with a thick tar/gravel  roof.   I would really like to enclose it for a wood shop so I can get all of that stuff out of the garage.

To enclose it I am debating my best course of action balancing difficulty and cost.  This spot is not visible from the street and I am surrounded by family so permits are not an issue.  Stick frame for the walls is the way to go, but Im not sure what to do about the base.   I am debating two main options for the floor, but I would love to hear any other ideas.  Do I pour a concrete foundation?  Do I build a plywood topped "deck" on concrete blocks under the carport?  Would I attach the deck to the posts or pour the foundation around the posts?  

Since the structural posts are already set on what we will assume are adequate foundations, I would just excavate a trench 12" wide by 32" deep (24" if you live in the south) from post to post.  Put 2" EPS rigid insulation along the inside edge of the trench.  Then, pour your floor slab and fill that trench at the same time, to make a haunch that is integrated with the floor slab.  If you're feeling extravagant, put a piece of #4 rebar along near the bottom of the trench.

The real issue depends on the surrounding grade.  I assume it is more or less flush with the carport slab level.  Technically, the bottom of your infill framing needs to be 8" above finished grade.  You can do this by laying 1 course of concrete block around the edge (fill the cores with mortar), or you can form up an 8" x 8" curb and pour that with the floor slab as well.

Remember to use a PPT bottom plate where it contacts the concrete or masonry.

I should mention that the soil at my house is only 8" deep.  my house is  on top of a limestone bluff.  Would I be okay pouring the concrete on the limestone or otherwise putting rebar down into the stone and tying the concrete into it that way?

If it's really bedrock limestone, then yes, I'd say you're probably fine just haunching the slab down to the rock.

How high above grade is your intended finish floor level?

In reply to Duke :

There is a pretty good slope from front to back.  The grade drops 11” from the front of the carport to the back.  So the higher I make the floor level the higher I have to put the  floor at the back.  I am thinking this will require a ton of concrete if I pour a full concrete slab.  That was the main reason I was thinking about putting down concrete blocks and building the floor on top of that.  

If you're bearing the floor on something like a perimeter foundation, that makes things much more complicated.  It also sounds like you don't have the depth required for a crawlspace. 

I would suggest setting the the floor a couple inches above the highest grade point (plus the curb I was describing above), or if feasible, 8" above grade (and eliminate the curb).  Then backfill the floor area with compacted gravel to the depth required and put a 4"-5" slab over that.  Haunch the perimeter as I recommended above, as deep as you can before hitting the underlying rock.  Instead of the vertical insulation at the haunch, lay it flat under the slab for 24" in around the perimeter.  The top face of the insluation should be flush with the top face of the gravel fill so the bottom of the concrete slab is flat.