[villagetinker]

roggie49,
IMHO, go to the Sumter County Building department (Pinellas Plaza), and explain what you want to do. They have been very helpful to me in the past. They will explain what you can and cannot do, especially with respect to raising the floor. I had a long discussion on that item and came away so confused, that all I can say is go and ask for yourself. Bottom line, a lot depends on the design and construction of your existing house. They can look that up while you wait, and then let you know what is acceptable. There may be other requirements, like electrical (flood lights, and receptacles).
Once you have that information, then you can make up a detailed list of items to be included in the project. Be sure to ask questions about future plans, like tiling, etc. There are LOTs of options, plastic (for the windows), glass, low E glass, wood, vinyl, aluminum, etc. Make up a detailed list of the items that are absolutely required, then have a list of optional items. Then when you present your list to the contractor request a detailed cost estimate, and a schedule for those payments. The last payment (at least 10 to 15%) is to be paid AFTER final inspection by the building inspector, and your own inspector (if you desire).

If the builder requires a down payment, then I would request that they use a credit card, as this will give you some leverage if there are problems.
I hope this helps, and send a PM if you want to discuss in detail.

There have been several threads about lanai enclosures on this site. Search these out, look of info on the products (what works what does not), ignore any comments with regards to adding concrete, A/C, etc, as most if not all of these have changed with recent building code changes.