I don't recomend buying this exact coop, because the quality is not that great. I learned that the hard way. It says its big enough for 5-6 chickens, but I'd say 3 maybe 4 tops. At least it can give you an idea of the size and style.
I would recommend reconsidering the "small coop" thing if at all possible, and going for something larger and walk-in size. Reason being, it is real hard to winterize a small reach-in coop for these sorts of temperatures... you pretty much end up having to sacrifice air quality or draftiness or temperature or several of the above. A larger volume of air -- even just a 4x6 walk-in coop -- is FAR more stable and easier to ventilate. You can have a smaller roost compartment inside of the larger coop to concentrate the birds' body heat.
If you are really set on a small reach-in 3-bird-size coop, I would suggest making the run roofed and partially-wrappable in heavy duty plastic, so there will be a less windy area to ventilate from.
But a larger, and larger-air-volume, coop will really be much easier to manage.
Hello, we have a 4x8 sheet of plywood as the floor with cement blocks to keep critters from digging under it, also to keep hens from laying under it.
Then the walls are about 6' in the front, 5' in the back. It was built in a existing shed, tar paper on the back side to help stop breeze. I use the deep litter method, it has an "in law" appt if someone is ill or needs time out, and this holds 5 hens in a Maine winter.
I do not insulate, yet I do use cardboard on the ceiling to help insulate from the cold that likes to drop down.
The outside wall you see is made of wire with heavy clear plastic over it so the girls have a tad bit more room on sunny days- or inclement too.
This winter I allowed the girls free access to outside except on bitter cold days, and they were very healthy and they do have CRD that needs air that is drier then a wet environment with heated water and manure.
Then we have a hutch that holds 4 bantam Cochin's. The Living quarter is styrofoam insulated double walls.
The "run" has hardware cloth but we put heavy clear plastic over it and it was plenty warm for them, I did use a heated water bowl.
I am pretty impressed by the coops that members have on here. I'm proud of ours, but that is sentimental cause DH made 'em!
I have a playhouse coop also. Almost exactly like the previous poster.
This is a picture from last summer.
I winterized it because of all the snow we had. I enclosed the covered run with greenhouse twin wall polycarbonate, and added a second small run along the back . They now have additional run space for summer weather. I had planned to make the polycarbonate into storm windows that could be removed but it only gets hot here 1 month a year.
As the saying goes..."If summer falls on a Saturday we have a picnic."
The birds spend a lot of time in the greenhouse part, which I heat with lights. You would have to realy heat it in your neck of the woods. I also insulated the sleeping part, added a dropped ceiling in there to reduce the amount of space they had to heat with body heat, put in a hundred watt light bulb, and slapped two layers of bubblewrap over the outside of the window and taped it down with duct tape. I suggest you also make the sleeping quarters fully insulated. (don't forget to insulate the raised floor).
Realy I do agree with Pat that a bigger building would be better, or let them have a small section of another building like the garage.
I keep saying I will get out there and take pictures as a greenhouse coop goes mine is pretty neat. If I can get to it I will update my post.