The more space you can give them indoors (for winter purposes) the better. Many folks on this site recommend a minimum of 4 sq. ft of housing space, but if you can give them more then by all means do it!! Folks who don't get winters can get by with less with no problems, because their birds truly are only inside to lay/roost year-round.
My girls had about 8 sq. ft (taking feeders/waterers out of the equation) of indoor space last winter, and they STILL were quite cranky by winter's end (and I opened my pop door every day to give them opportunities to go out). Folks who have tight spaces often end up with feather picking issues and even cannibalism over winter time. Let's face it, if you were stuck inside with your entire family all winter, you'd all fare better if you lived in a 1600 sq. ft home rather than a motel room, where you're in each others' faces all the time.
Ask anyone who has had both at different times - ample room or limited space - through a snowy winter - there's a noticeable difference in chickens' behavior.
Adding roosts, shelves and such can help as a boredom deterrent. Covered runs and windblocks can help tons in winter time too. Chickens do okay if they're able to get out and about all winter, but icy winds aren't good, and most chickens don't want anything to do with snow.
As for desiring a small coop in winter - NO WAY. You'd still want ample floor space. A huddle box within the coop or something similar can be used in those cases.