I actually didn't think about ventilation at all when building. But fortunately I read the ventilation article by Aart and another member (who's name escapes me) is always talking about the importance of large roof overhangs to keep rain out. Now that the coop has been finished and functional for several months I can report that so far zero rain has gotten in, and it is alarmingly dry inside (I have no food or water inside, all underneath). So both the ventilation and the overhangs are doing their intended jobs.
ETA: I'll be incorporating the in-coop brooder a few posts above, even though I currently have no room for more chickens.
ETA: I'll be incorporating the in-coop brooder a few posts above, even though I currently have no room for more chickens.