Should I leave some of the coop walls open as just hardware cloth? It gets HOT here, triple digits in the summer. But doesn't usually get below freezing in winter.
A "California" Coop is closed on three side with the North side open and covered with hardware cloth and a roof that stick out to catch the rain. There should also be vents at the top.
Ventilation is very important and keeping them out of the wind in the winter is important as well. You do not need insulation. Chickens are their own little insulators...
Hangtown farms and Capayvalleychick have built some recently.