Those little coops are tough to ventilate without opening too much and getting a draft on your birds. Your best bet might be a simple roof vent. It will let the warm humid air out without letting wind-driven snow in. The door probably doesn't have a weather seal, so it should be loose enough to let enough fresh air in.
Thinking this style: place on the roof that is facing away from the predominant wind/storm direction.
I have a little coop like that that I use as a brooder - not exactly the same as mine does not have the peaked roof, but similar in size. I have it in the barn.
Thinking this style: place on the roof that is facing away from the predominant wind/storm direction.

I have a little coop like that that I use as a brooder - not exactly the same as mine does not have the peaked roof, but similar in size. I have it in the barn.