I live in New Orleans, we dont even have winter. We have summer, hotter summer, hottest summer, and less hot summer with 99% humidity all year...
Anyways, underneath my 14x20 foot graceland shed (on 1ft of blocks) must be really cool! The dogs go in the shed (has window a/c) but the chickens go under the shed and stay there from 11am till 3pm. So I left them an open space to go under there freely but not large enough for the dogs to fit.
so, a low to the ground structure that blocks all of the suns radiant heat would be the best protection from heat.
also, they love moist sand in the shade they will flap around and bathe to keep cool.