I have 2 girls who "roost" on top of my metal nesting box, it's slanted and they put their feet right up at the top and have about 2inches between that and the wall!
I've had up to 6 "roosting" up there but these 2 have just never left that spot. My other "roosts" are about 12 inches from the wall and plenty of space for all of them and more so it's not that these 2 don't have anywhere else to go, they just like this spot!!
