I suggest a vent at the top on the East and West sides. Make your window to the South so they can get some natural light in
during the winter months. If you have it in an open exposure to the South this gives a little bit of passive solar as well. If it is gabled, the heat will rise to the top. Wind will pull the air through from one end and out the other vent if it is properly aligned with East/West.
What do you have made already, can I ask? I find it easiest to use metal roofing materials, less weight and less heat radiating in Summer. I would suggest double wall instead of insulating since insulation can make it too warm and then allow moisture build-up in Winter from birds pooping and breathing.
I would got bigger not he window too if that top rectangle is the window, but that is my personal opinion. I do think birds are happier with natural light as much as possible. A Window can mean using clear roofing material over the opening too. In fact, I just did this to a small coop where I used to have an access door to the nests I originally had in there. The birds loved the light coming in there without having to be exposed directly to the outdoors to get it. There is enough airflow around the ripples in the clear material too that it allows some ventilation without having draft. I can take some pictures if you want me to show you what I mean. In fact, I used that for a few coops this year to give them a window. to brighten up the coops. Of course, you can always go with the barn windows, which can be found at Fleet Farm for the best prices. I have used the vinyl sliding windows in the brooder house, which I would not recommend since they get all skanky in the tracks and are hard to clean. I opted for awning windows for the new building I started and plan to house rabbits and either bantam or started birds in.
I have made lots of coop building mistakes, so I can offer things to NOT do as well as things TO do
