You don't say how old your chicks are. I've had a broody take her chicks to the roosts at 1-1/2 weeks old in the summer. I've had them wait until 4 weeks at times. I'm not talking about them playing on the roosts during the day. I'm talking about them sleeping on the roosts at night.
I've had brooder raised chicks start roosting at 5 weeks. I've had brooder raised chicks start roosting at 12 weeks. Others have posted that theirs take a lot longer to start roosting.
Each chicken is a living individual with its own personality. Each flock has its own dynamics depending on a lot of different things and those dynamics can change over time. There is no definite time limit or schedule for these types of things. They will roost when they are ready to roost. Until then, expect them to sleep together on the floor, not because they are cold, but because they like each other's company.