I will give you a suggestion based on my experience. I have kept poultry in the Rocky Mountains of Alberta for 5 years now (-50 F average cold temps) All kinds- ducks, chickens, quail, guinea fowl. All kinds of coops- 3 sided ones, tractors, sheds.
You'll want to start of by picking a cold-hardy breed. Ducks and quail are cold hardy. Wyandottes, Chanteclers, are both hardy- any small-combed breed is cold hardy. Brahmas are hardy, but their feathered feet cause snow and ice (moisture) to accumulate on the feet (one word FROSTBITE).
Next you'll want to consider an alternate location for a coop. The no-sun is a big issue. If you don't have an alternate location, I would look into a different style of coop. Make it walk in, and suitable for deep litter method (a great way to conserve heat).
Make your roosts 2x4s, 4" side flat, so the birds can protect their feet in the cold.
You'll want the coop to have 4 square feet of space per bird, especially if they will be locked up in winter. I wouldn't do 6 or 8- in cold weather like ours, you need to sort of squish it a bit. It's still humane and my birds do fine.
Build it with double-wall insulation using fiberglass insulation on the walls, floor, and roof, as well as a vapour barrier. That will be the best heat conserver.
Wire it, or have plans for an extension cord. During those cold winter months, your adults may not need any heat (mine don't), but you will want a heated waterer or heat pads to prevent freezing eggs. If you want your birds to lay throughout winter, you'll also need supplemental lighting.
Make sure all your ventilation is closable. Trust me. Most folks on here who suggest ventilation have never been in temps like ours. I learned this the hard way. Yes, follow the one square foot of ventilation per ten square feet of coop space rule, but make your ventilation closable and openable. In cold winter days, you may have to close up the coop completely to conserve body heat- and if you do decide to heat, for whatever reason (I am right now, because I have 10 week old chicks), you'll want that closing option. Another great way in cold temps to conserve heat but provide breathable insulation is stuff hay into your vents during winter.
Don't make the vents high up. This will cause all the heat to escape. Fatal in cold temps. Make them close to the floor, away from the Northern side. Drafts don't equal ventilation. One foot above or below your roosts.
Look into space effiency because your birds will be so cooped up during winter. Nest boxes under roosts. Movable roosts. Great ways of keeping the floor space large.
Frostbite will happen for a variety of reasons. I have had frostbite happen in open-air coops so I say, shut up the coop if you need to. Try to avoid food and water inside the coop. Choose small combed breeds.
I don't use heated waterers. I prefer providing free-choice snow, and then making 1 or 2 trips per day out to the coop with warm (not hot or steaming) water in a rubber livestock pan.
