5 weeks is pretty young yet, for chickens to start roosting. Mine took several weeks to learn how to do it. After all, it does involve balancing while asleep!
First, they got up on the roosts during the day, to look around, perch there and see what's up. But they slept on the floor of the coop.
All together, almost in a pile.
After several weeks, when they were around 12 - 15 weeks old, one of them started to roost at night. Pretty soon another did, too. And then they all did it, but they were close to 18 weeks old by then.
I didn't put any of them on the roost bars, myself. I just let them learn how to do it by themselves, free choice. Eventually all of them are roosting.
All of mine, including the BO started sleeping on top roost at around 9-10 weeks of age. They all like to sleep on the same one, even though there are 3 roosts to choose from.... They all figured it out for themselves and are all up there by 6 pm every night.
During the day, when in the coop, they still prefer to sleep in a pile in the shavings
We have just finished their run so I am excited to see if they put themselves to bed tonight!