I'm having the same sort of problem. My chickens are about 10 weeks old and they will not roost in the coop but perfer to pile up in the corner of the run. Every evening I put them in the coop in the hopes they will catch on, but no luck so far. Definitely open to any suggestions.
These birds are all just babies yet. There's no reason they NEED to roost. They're young enough they still like the comfort of huddling together. They'll roost when they're ready. It's no big deal for them to be sleeping on the floor still, it's quite natural.