I wonder if window screening might hold up better for you than fabric? I think there's lots of different sheer fabrics you could probably get, but not sure if they'd stand up to a typical Florida thunderstorm without an awful lot of reinforcement. If the price per yard is similar enough, I might go for plain old window screen: still lets in some light and water, but will offer some shade.

I got shadecloth to cover the orchid shade house from International Greenhouse Company. Since I needed a lot - the shade house is 10' x 20' - their price was the best. The shadecloth is of great quality and has lasted for at least 4 years, through Florida's rains and thunderstorm.

For smaller quantities, Hope Depot or Lowes are probably the best bet?

I agree that IGC (also known as Greenhouse Megastore) has the best prices and the best quality I have found. True shade cloth is VERY tough, many many times tougher than screening used for porches and patios. Plus you can get it in varying degrees of effectiveness from 30% shade all the way to 90%. They also have pre-cut sizes with taped and grommeted ends which can make attaching it to a structure much easier.

The sail shade with high denisty polyethelene works OK for me down here in the caribbean.

I got some from Lowes that did really well when I lived in Lake Havasu City, AZ ( super hot 120 in the summer, and dry as a bone) once I moved here I gave it all to the chickens lol to shade thier run. I've had it for 4 1/2 yrs and it is still holding up.