Well, it's not pretty, but I figured out a way to keep the girls cool on the especially hot and still nights we've been having lately. I check on them at night when it's exceptionally hot, and quite a few times I found them panting and holding their wings out because it was hot and humid with no breeze whatsoever. I started freezing water bottles to place on the roosts beside them, which they seemed to appreciate, but (of course) they ended up getting knocked down onto the floor. My coop has a peaked roof and the top roost is about 2' from the highest point of the roof, so I stapled elastic hair ties to the roof so that I could mount the frozen bottles. Two ties per bottle to keep them level has so far kept them snugly in place, and the cold air sinks to give the girls some relief from the heat. It isn't pretty, but it's cheap and is helping a lot, nobody was panting when I checked on them last night.