We have cage covered vent holes on each side at top. Can add more if needed. There is a small window on one side that can be opened. And doggy door converted to let them out , we added a hook so it doesn’t fall down, but door latches close when completely closed - I currently lock them in at night and close window for safety.
They need ventilation 24/7/365.
Cover any openings with 1/2" HC for predator protection.
This.
The usual guideline is a minimum of 1 square foot of permanent, 24/7/365 ventilation per adult, standard-size hen. This is best located at the top of the coop, because heat and ammonia both rise.
Ventilation is just as important in cold weather as in hot weather because the moisture they generate from their poop and their breath has to escape so it doesn't freeze onto their combs and cause frostbite.