I don't know what size holes you made but something like this would help
http://www.amazon.com/Air-Vent-Inc-...1372_1_18?s=hi&ie=UTF8&qid=1442499242&sr=1-18
Those are for two inch holes.
Or you can make your own version of a louvre cover using strips of wood or metal and actually increase your ventilation area.
Either way, though, turning the coop may be a good idea so that you don't have strong winds trying to rip through there, especially once it starts getting colder.
http://www.amazon.com/Air-Vent-Inc-...1372_1_18?s=hi&ie=UTF8&qid=1442499242&sr=1-18
Those are for two inch holes.
Or you can make your own version of a louvre cover using strips of wood or metal and actually increase your ventilation area.
Either way, though, turning the coop may be a good idea so that you don't have strong winds trying to rip through there, especially once it starts getting colder.