My current batch of six, six week olds, are still sleeping in a pile on the floor. This is their second night in the coop. I have no doubt they'll decide one day soon that roosting on the perch is a better place to sleep, if only to get out of their poop.
The more complicated issue is teaching them to go in and out of the coop come morning and night. The problem they're dealing with is six older sisters who, while bunking in their own partitioned off section, won't let the tykes have free passage. Each group has their own pop hole, and that ought to help, but the tykes need to muster up the bravery to get by the big hens and into the coop.
While they're still this small, I'm gathering them up and carrying them inside, and refereeing their exit in the morning. A lot of it involves maturity, learning, courage, and we just have to know when to help and when to leave them alone to learn things on their own. It's a delicate balance. But it's fun, too. They'll signal what they need from you. I knew I had to carry them inside tonight when I saw them standing in the gathering gloom in the pediatric wing of the run (where the big hens can't bully them) and frantically screeching their heads off.