Alright, I've got two roost for my chicks in their pen that's on the grass and the only one roosting insists on the waterer and the feeder. I'm also wondering when the other ones are going to start roosting as well.
Is the pen for daytime use or are they being kept there all the time?
Chicks that young usually won't roost for the night on a roost, most likely they still pile up. Water and feed containers are wider and probably more comfortable to perch on.
You could try moving the containers further in and lowering the perch a bit to see if they will take interest. I've found they will "play" on roosts during the daytime, but don't do much roosting for the night until they are about 6wks old.
This pen is just for the daytime. I put them in the pen about 11am or 12pm because the mornings have been a little cold. Around about noon give or take; it warms up enough for them to be out. In the evening about 5pm I put them back in the brooder box. Yes, they still like to pile on top of each other; sometimes in 2's, 3's or all 4 of them. One perch isn't very high at all, and the other one is about the height of the waterer or feeder.
Nice! It's wonderful to have an daytime pen for chicks. Is your coop and run ready for them?
Chicks do love to perch on the containers, but will usually out grow that (have to poop in the food/water too!).