My four one-month-old Buff Orps have had a roost in their brooder since they were about 2 weeks old, and they have been sleeping on it for almost that long. I put it in there just so they had something to play on and get used to, and it did the trick! I just moved the brooder from the house into the coop, and even though they can come and go from the brooder cage into the open coop as they choose, they still put themselves back in the brooder and on the roost at night. They even did it when I opened the pop door into the run! I generally go out around 8:30/9, when it's not pitch black, but getting pretty dark. I think the brooder is their security blanket.