It depends on your birds and your set up. I keep mine at about 6 inches, some I even have a ground level. Brahmas aren't known for their ability to fly, generally their size and weight keeps them pretty close to the ground. I've seen them get up on roosts that are about 3 feet high, so they can do it. I don't like mine to get to high up because I worry that they will injure themselves when they get down. I've also seen some folks put their boxes on a higher shelf and have a ladder up to the boxes. Like I said, sort of depends on what you're set up is.My Brahma has been at point of lay for over 2 weeks and she is now 27 weeks and doesn't fly at all. Any advice on nest box height and size? My others have chosen a milk crate they fly up to. Thanks!