Hi Suzy!
I can't think of the style name... but if I were going with a new building I would do the 3 sided open end, with a completely open 1/2 in hardware cloth, sandwich screwed not stapled, on ALL openings. It should be just as predator proof as anything else, but completely solves ventilation problems which oddly are KEY in extra cold climates.
Sounds like you have the gauntlet of predators... and rats are NOT the least of these. I've seen WAY too much recent posts about rats eating chicks and full grown hens ALIVE!
I know the coop style I am describing IS listed under the learning/article section here on BYC. Sorry I can't be more exact, but hope it helps anyways.