My chickens are pretty much outside 24/7. The entire east side of our coop is open - covered by welded wire. There is a good sized window on the west side, too. We will be covering the west window with a tarp this weekend, to cut down on the wind and keep things a little warmer. We debated on covering the east side, but the chickens love to sun themselve there. Once our run is completed, we will probably enclose the east side of the coop, but will open the door into the run every day. In my old henhouse, we never closed the door into the run, and rarely had a predator problem. (The dog we had back then was very vigilent about guarding what she considered to be her babies!)
I just figure that the chickens need all the sunlight and fresh air they can get. Shutting them up in a coop every day can lead to excessive moisture buildup, which is a recipe for disaster.