If they're used to being outside, they may not like going in the coop for awhile. When I got my 1 day old chicks last year, they lived in my house for awhile then outside in a giant coop with lots of branches and perches they liked to sleep on. Then something got in through the top netting and killed one chicken, so I redid their coop under my deck and my dad spent forever making them a gorgeous house. It's a 3 foot tall free-standing house on a 3 foot tall open base, inside a 12 foot tall 10x10 coop. They have playroom under the house and can fly to the top. Since the roof of the house is taller than the roost bar inside it, they sleep on top. They will go in it and use the nest box like pros, but don't even acknowledge that they are supposed to go in it otherwise. If I know it's going to rain at night I have to go out and grab their sleepy butts from the top and plop them inside to keep them dry. Your set-up may be completely different of course, but if they're used to being outside they might not like feeling confined for a bit. I'm sure they'll get used to it in their own way though, like my brats did.