Well Freedom, you are so fortunate to be a contractor! You will be able to figure out if your roof structure can handle the weight of sand/soil on your roof – and if it needs help – you are blessed with skills to fix it! Good idea. If you can build something about 4-5′ tall around the edges of it, I would think that would be even better. Why? 1) hide it from street view, 2) the plants will dry out less because it will help block the wind/steady breezes you get the higher you grow and that S FL is so well known for. Also, 3) you will have something to attach, support growing things vertically much easier like vine plants.
You would just need to install a good drip irrigation system. If you can support the roof enough, you could install a rain barrel or two and collect the water from your roof into the rain barrels. If the rain barrels are raised high enough, the gravity will feed your drip system without electricity/pumps.
Here is a video of a rooftop garden that I think, IMHO would work well for you there. With something/structure to attach shadecloth as needed you would be all set.
I know you grow things, but I thought this PDF from Broward County was pretty good for the area, in case in might be of some small help.
Gardening is my favorite subject!