Glad you found our thread! Hoop coops are great, very flexible.
Tarps do block the sun's rays. If you find it builds up too much heat, consider replacing it with a double layer of good shade cloth, it'd probably repel rain staying bone dry inside and allow some of a breeze. I had a coop made out of the arc of a 14 ft trampoline and the 2 layers of shade cloth kept it completely dry. I was surprised, but I think it was the curve of the arc that allowed the doubled shade cloth to do this. Also, if you can have a fan, you could have a small outdoor swamp cooler instead. Even a fan probably won't be enough for Yuma, bearing in mind that even Andalusian chickens start to feel heat stress (panting, wings out) at 90 degrees. Most breeds show this same stress at 80-85, let alone 100 or 120 degrees. These coolers are about $150 probably by now. (oops, they've gone up! the one below is similar to what I had in black canyon city
https://www.homedepot.com/p/Hessair...er-for-500-sq-ft-in-Sandstone-MC18S/317051471
That way you'd worry a lot less. You can also put a small thermometer in the coop, the kind that registers its hottest and coldest reading, and you'll know if the coop gets hotter than outside or not, at any point in the day or night. Speaking of, roosttime is the heat of the day in most areas of AZ where it gets hot, so late afternoon sun will be very important.