I had the exact same problem and it was driving me crazy with worry. I was afraid something would break into the enlosure while they slept on the outdoor roosts. My DH had gone to a lot of trouble to get the coop in shape too and I think it hurt his feelings. Well, I think I've solved the problem. I think the chickens were afraid of the coop because it was dark and unfamiliar, so I went to Loew's and bought a small hanging work light (low heat, cool-burning type, yellow plastic housing, looks like a hanging flashlight) and turned it on in the coop as it got dark outside. This seemed to do the trick and now they all have just learned to go in and get on the roosts when the light comes on. (Even the rooster, who was the last hold out having been a stray "tree-rooster".) After they are all tucked in, I turn the light out. This weekend I'm getting a timer. Now they put themselves to bed at dusk. Both me and the chick-chicks are very happy with the new arrangment.