Help. We want to close in a 12x20 carport. We will only have to deal with 2 walls. There is approximately an 18 inch drop from the interior level of the floor to the concrete slab of the carport.We want to build up the floor about 10 inches but not the same level as the interior. Is it OK to build a standard joist-constructed floor directly onto the slab or do we have to build a block foundation on top of the slab and then build the joist floor onto it? The slab is approx. 2 inches above ground level. There does not appear to be any problem with drainage or water seeping onto the slab. Also would there be any problem with codes in this type of construction?