I know It's an old thread, but I figure with winter knocking at our doors I would add my suggestions.
Here are a few things I learned last winter.
1. Door clearance. Last year the doors on my coop caused big problems we got into 12"+ of snow, it piled up and made closing the coop a big problem. it would warm up and the mud and snow would get between the door and base of the coop and turn rock solid. When I built my new coop I made sure this would not be a problem, I also just raised my gate into the main yard up higher to clear the snow.
2. as mentioned, heated water bowl saves on time and damage to waterers
3. An easy to clean coop makes a huge difference. My previous coop was very difficult to clean and my first winter it basicly got out of control, the snow wasn't even off the ground when I started constructing my new one.