Instead of a roosting bar, I put small logs (pieces of firewood) right on the floor of the brooder, starting at 2 wks of age. I start with about 2 inch diameter logs, then increase gradually, so they gradually exercise their legs/wings. Right now I have 2.5 wk old bantams and a 4-5 inch diameter log in the brooder. The added benefit to logs is you can get a new piece from the wood pile everyday, so it never gets poopy, and each one, with different bark and lichens, is a bit of a novelty. They love to peck at the bark and lichens, which helps keep them from pecking at each other. If you try this, just make sure there are no sharp edges where they can cut their feet. I sand the cut edges of each piece of firewood, and use whole logs rather than split pieces of wood, so the chicks won't get splinters.