Hi, it's nice to have you here with us! I used to keep a flock at our old FL home and the heat + humidity is a real issue. @TwoCrows has given you a good link to check out, hope it helps!
Shade, shade and more shade will help them keep cool. If you don't have natural shade (trees etc, then cover an area with shade cloth (as a run cover= perhaps) to cool the air around them somewhat.