The vent I am talking about is at the top of the coop and stays open all year round to let air in, even in the winter. There are windows on three of the walls that can open in the summer and then can close in the winter. I checked out a book from the library today that showed an open vent that was 5" That really helped. I can stare at a tape measure but cannot always get the distance in my head of how it would look on a finished coop.
In the picture I posted he had a board in the top with holes cut into it. But I think just having it open would be better and more ventilation.
Sorry for all the questions. There is so much info out there that it gets confusing. And some of them just do not seem to have direct answers. Such as the ventilation. Everyone agrees there should be a lot of ventilation but no one says how much "a lot" is.
From what I read there needs to be 12 inches head room between the roost and the top of the coop. So would 18 inches under an open vent area be enough for them not to get a draft in the winter? I know the air flows along the top and out the other side, just want to make sure it is not blowing on the chickens as it goes across.