Originally Posted by Joba Fett
With idiodic responses such as this, no wonder these so called DIYer's get people hurt.
And just what made that an "idiotic" response? Think! First, the roof is already supported by some kind of structure, so the only load being imposed on the slab is the wall to close it off, which weighs a hell of a lot less than a car. Second, the wall load is dipersed across the length of the slab and is static, rather than the concentrated, dynamic load that the car tires impose. Much depends on where the OP is located. If he has to worry about frost conditions, and the slab is floating, that is an issue.
So far no-one has given the OP a good answer to his question. To the original question: First dig down along side of the fslab to see if there is a footer and foundation wall under it. If so, you can build on top, if not you may need to place those items and size them according to your local requirements for soil conditions, etc. Whether you need a building permit for this work depends on your local community. There are a few questions you'd need to answer before anyone here could give you further direction. Do you intend to step down into this room? Or build the floor to match the existing house? Does the roof of the house extend over the carport area? Or does the carport have it's own roof butted into the end wall of the house? Adding simple exterior walls will add little weight, adding a floor system with joists and beams will add some concentrated loads to specific areas that you will need to address. You first need to do some research.