My brooder raised chicks normally huddle on the floor instead of roosting until they are around 10 to 12 weeks old, then they start to roost on their own. I think they just enjoy the company down there. I see no reason to force them to roost when they don't want to. Usually around 10 to 12 weeks of age, one or two will move to the roost at night, then within a couple of days, they are all roosting.
If a broody raises them, she usually huddles on the floor with them for about 4 weeks, then she takes them on the roost at night. They are usually fully feathered out at 4 to 5 weeks, so they do not need to stay huddled on the floor for warmth. I have no idea where Wilbraham is. Sounds like it is an English-speaking country somewhere in the world, but I have no idea what your weather is like this time of year. Since yours are 6 weeks old, they should be fully feathered and should not need any supplemental heat unless it is extremely cold where you are right now.
I'd go ahead and make the adult roosts. They'll enjoy playing on them during the day and move onto them for roosting when they are ready. It certainly won't hurt anything to be prepared. Just because mine wait until they are 10 to 12 weeks old does not mean yours will.
Good luck!