Set them high ! You can always back off if needed. In Florida you should be able to find a used poly-house without too much effort. Find a local greenhouse and ask if they have any Grower Talks or other greenhouse magazines, there's tons of ads in the back for stuff.
Another good source of ideas is the Ball Red Book. Check your library to see if they can find you one to look at.
Don't forget that alot of materials can be found at the local farm supply stores too (water lines and mist nozzles used for chemicals, etc..).
Take your time and do it right or you'll be fighting it for a long time ! Have fun !