is code enforcement. Each manicipality has its own set of rules on this construction, so you should entertain the question to them.
Now, if it was mine, I would build a deck directly on this slab to get to the height you desire. Anchor this down to the slap with Redhead anchor bolts or similar. You do not need too many.
Use 2x6 PT joists 16 or even 12 OC for a non rocking flooring. Cut any trap doors for access to some area if needed. Lay down Rat bait before you close it up also. Plan ahead with trap doors so you wont have to do it later.
If water could be a problem, then build the joists on solid 4 inch wide cinder or haydock blocks to keep the water off the joists just in case. yes, even if the joists are PT wood material.