Chicken Doors?

K, We have a roof on, sorry no pics yet. We have started discussing the windows and ventilation. For those of you who don't know, my husband is an engineer. Nuff said? It has been a long process designing this coop. Does anyone out there have any advice on coop windows, ventilation and chicken doors? Anything you've done, anything you wish you would have done, anything you would change, anything you've seen that you thought was totally cool? Please advise.