Is there any place you can put your coop where it's in natural shade? Shade and lots of ventilation are key for those of us who deal with hot summers.
We live in North Texas and it gets 100 degrees plus regularly here in the summer. Our best coop is in the part of the yard that is shaded from afternoon sun by trees. It has a radiant roof sheathing, and it's also insulated with fiberglass and foam board (I used up bits and pieces of what I had leftover). I insulated it primarily to help retain heat in the winter, but I think the insulation helps some in the summer. The inside of the coop heats up more slowly than the outside in the summer.
The coop is 8' by 8' and has about 32 square feet of ventilation from a combination of vents at the tops of walls and windows lower down at roost level. By the end of the day, the inside of the coop doesn't get any hotter than the ambient temperature outside in the shade, which is about as good as I can hope for in the summer.