What can I do if......

What are you using as a roost? If they've never had access to a roost before sometimes it take a while before they'll use it.

 

I had to teach mine to roost - they wanted to stay in their cozy pile on the floor. I picked them up every night and set them on the roost until they learned. It might be that hatchery chicks have this problem, with no Mom to set them an example...

 

is it round they don't like round roost's to sleep on they should have a 2x4 unless they are bantams then a 2x2 will do, I learned this when I tried using bamboo poles it was ok for day time but at night they didn't want to roost on it.
and have you put golfballs in your nest or something resembling an egg that will give them the idea. and you can try making the nest boxes darker.

 

I try multiple level to see which one they like the best One of my roos found an old abandned terracotta pot and decided to sleep in that instead

 

I just posted this same problem. Mine love the floor of their coop. I decided to reposition one of their roosts a little lower and this morning it was obvious they were on it (poop marks on it that were not there earlier). I don't think this means they will stay off the ground completely because they like it, but I know they are using the roost. When I went to close their coop door tonight, once again they were huddled together on the floor of their coop by the door. I think they will get up on the roost when I don't see it.

Don't worry about it too much. I decided that as long as they seem happy and healthy, where they sleep is just personal preference.

Good luck.