Chickens need to be dry. Warm is less important. Airflow is vital. I know my climate is different, but I use polytunnel bars with white plastic sheet instead of clear plastic, to stop any boil-in-a-bag issues during the day. The "roof" stops stops 3 feet above ground to make sure there is lots of air flow, and it is open at either end. Wooden bars for roosts, and thats it: nothing for mites to live in. The plywood nesting boxes are a problem with mites, but what can you do? They are separate to the roosts, and lower down. It's ugly as sin, but the chickens have survived 15 years so far.
Turkeys don't like being inside at all, and roost on the bars outside in all weathers.
Foxes are a problem. Electric fencing works. A dog locked in with your chickens helps, too, as long as it doesn't learn to eat eggs or chickens. Completely covering the pen with wire also helps - see chicken tractor designs for hermetically sealed, mobile coop designs. I tried this, and gave up after a fox emptied the coop twice - 20 chickens at a time. Back to Fort Knox security and no more free range chickens. If only the chickens would agree to stay in...
