There is a guy on one of the homesteading groups I belong to that dug down 2 feet, then built earthbag walls up another 2 feet and roofed it. He's up your way near Quartzite. He says in the summer teh chicken pit is around 15 degrees cooler. The hardest part was teaching teh chickens to go inside when it got warm outside. He is now building a larger stand up coop in the same way.