When I added to my flock, I built another coop so that all would have the appropriate amount of space in the coop. When the new birds moved outside into their coop, they were kept inside for two weeks to make sure that they knew where home was. They spent 30 days in their run adjacent to the other run to get to know the other birds or whatever happens when you do this. When the door between the runs was opened, they all mixed.
For several weeks they would go up onto the porch of their coop to sleep. When they got too large to sit on their porch to roost, they moved to the porch on the older coop. It is wider than theirs. After while they got even larger; and they moved inside the older coop to roost. One by one, they moved so that soon there were none on the porch at night.
I soon relented and added more roosting space in the older coop. Now all ten are roosting in a 4x8 coop.
The new coop is unused. No one roosts in there, no one nests. I started to use the coop for storage of bedding and such. But, it is there if I need it.
Chris