If I am correctly understanding that you have 11 chickens in an 8x10 coop, they will not heat it up too much from their body heat, so that would not be a big concern in my mind. And anyhow you'd have lots of ventilation open at night when they are in the coop, right?
Whether it's useful to insulate in a hot climate, with the intention of keeping the coop cool, kind of comes down to three things: how much of the day is it hot vs cool, how well does it cool off at night, and will the coop hold enough coolth long enough into the day to be worth it?
If your temperatures drop quickly as the sun gets low, and get pretty good n cool overnight, then you can do a reasonable business on throwing open all the (lotsa) vent openings and windows at night, to cool the coop down as much as possible (just like you would a house), then in the morning shut the vents and windows and rely on insulation to hold the coolth.
However if your nights are generally warm, you may not be able to cool things off thoroughly enough to create a sufficient "coolness reservoir" in the "bones" of the coop to make insulation do you much good. Also, if the coop has little htermal mass (is small, and/or has raised floor, and/or is made of materials that are poor heat sinks) that will reduce how well you can get the coolth to linger, even with good insulation in place.
So, I dunno, it depends.
You want to have lots of openings you can throw open overnight to let cool air in, REGARDLESS of whether you insulate. (With predatorproof screening on them, obviously). The only thing insulation would really get you is (potentially, if circumstances are right) to make a sort of naturally airconditioned coop for the chickens to hole up in during *daytime*, at least for the earlier part of the day.
Dunno if that helps any, good luck, have fun,
Pat
