My isa browns have never roosted other than for a little while when I put them there, they sleep on the floor (in the nest boxes, when they were in the other house).
My "silly chooks" who are now in the big house get up on the roost, but they don't make use of the space, they huddle and sit on top of each other.
I wouldn't worry about where they want to sleep and just let them do as they please. If they are dry and safe, I don't waste any more worry than that. They are not going to co-operate with what they "should" be doing so I just accept that.