They stay out there at night?
Have you ever made them go in at night even when they were young?
Every chick I have owned the first couple weeks I let them out into the run, I had to make sure I put them back up at night. Then they learned that is what I wanted them to do.
Then hens I taught, will put themselves up at sun down. They are free ranged and I just have to remember to go out and shut the door to the run.
So take the roost down or lock them up at night for a couple weeks and see if that doesn't teach them to go inside. Also you might try giving them a treat at night in the coop.
Good Luck
Nick