Most people don't put roosts in their brooders, in which case it may take a few weeks for older birds to figure out "roosting" when they are moved to the big girl coop. However, you can give your young flock some practice with our Chick Jungle Gyms!
However, roosting behavior depends on the breed, too. Silkies are famous for not roosting, even when they're adults! Flocks of Silkies sometimes "roost" in a fluffy pile on the floor.