My brooder-raised chicks usually start roosting on their own around 10 to 12 weeks if there are no adults around. I've had some start roosting at around 5 weeks, some go longer before they start, but for most it's around 10 to 12 weeks. By roosting, I mean sleeping on the roosts at night. They'll play on the roosts during the day so they can get up there but don't sleep up there. If there are adults on the roosts they are not going to sleep with the adults but may find other places to roost. My broody-raised chicks start sleeping on the roosts when Mama tells them to. I've had some broody hens take their chicks to the roosts as early as 2 weeks so they can fly up there and they can sleep through the night up there at two weeks. Most of my broody hens wait until around 4 or 5 weeks to take their chicks to the roosts but each brooder-raised and broody-raised batch are different. Until the broody takes them to the roost they sleep under her on the coop floor at night.
My brooder-raised broods are typically around 20 chicks. I have a perch in the brooder for them to play on but they hardy ever sleep on it at night. They tend to sleep in a group on the brooder floor, usually pretty close to the heat even when they are warm enough. They seem to prefer sleeping in a group as if they were under a broody hen as opposed to sleeping scattered around.
My broody hens sleep on the coop floor with their chicks until she takes them to the roost. Some broody hens never take them to the roosts before they wean them, those still sleep on the coop floor by themselves. My brooder-raised chicks sleep on the brooder floor. Those same chicks go to sleep in a group, either on the coop floor or outside in the run until I train them to sleep in the coop, when I move them to the grow-out coop until they decide to sleep on the roosts. Some adults, like some Silkies that can't fly, never roost but prefer to sleep on the coop floor even if low roosts are provided. I fail to see the urgency to get them to roost before they are ready. You can train them to roost earlier but I don't see where that makes their life or yours any better.
I train mine to sleep in the coop for predator protection. I let them train themselves to roost whenever they are ready.