What is your climate like? How many days/weeks a year will you have snow on the ground and are bad storms common? Will you free range your hens? What breed do you have in mind and large fowl or bantam? If you get quite a lot of snow you will need 4sq feet per large fowl chicken so 7 hens would need 28 sq feet so a 4x7 coop would be ideal. If you are like me and have a mild climate (I'm in Ireland) you can get away with as little as 1 sq feet per bird but I prefer 2sq feet so a 4x3 or 4x4 coop would be great. This does all depend on the questions I first asked, calmer birds need less space, bantams need considerably less. You will also need a minimum of 10sq feet per bird in their run
I live in Massachusetts, so from December to march there us usually snow. I am looking for larger cold hardy hens and we might have 2 coops, one for summer and one for winter. Depending on what we decide, the winter one might be an A-frame that is 7x11 overall (coop and run), that is if we use our old swing set for the frame.
Hmmmm.... I live in Upstate NY and I believe my Winters resembles yours. I also wanted cold hardy birds and so I purchased four Barred Rocks hens. They fit that bill.... cold hardy. But I give them 10 Square feet in their run and I'm not sure how much per their raised house but it seems big enough. With my four BR hens... I couldn't imagine giving them less than 10 Square feet per hen because in Winter they don't get outside of the run too often and any smaller I think they would fight.
I just want to mention that if you're like me (and a majority of people on BYC) you'll get more chickens than what you start out with. Please take that into account. I just got two new chicks and I feel the need to add another run onto the other side of my coop. I always wish I had a bigger coop too, but I feel like the coop is adequate.
My chickens love their run, so I think more run space is more important than more coop space for me. My chickens only go in the coop to eat, sleep and lay. I keep the water in the run and they generally stay outside, even in rain. Anyway, always plan on more chickens (even if you don't get any) and you'll be fine.