Same here! I have a large Nestera that sits on a platform, three feet off the ground. The first 3 pullets slept in it and loved it. As the summer got hotter, I built an L-shape roost next to the coop but still in the very open run, an inch or two higher than the roost in the Nestera. They took to it immediately.
We added two more 7-week-old pullets in mid-summer, and once they were mostly integrated into the flock, they started sleeping in the coop. Even with temps in the 20's at night, the three olders still prefer the outdoor roost, while the youngers sleep in the coop. Sometimes they'll try to join the olders on the outdoor roost and are promptly chased back inside.
I'm working on a design of a sort of box-shaped coop that is large (8 feet long, 3 feet deep, 4 feet high) and would have, like, removable side panels so that in the warmer months it will be "open" (ie just hardware cloth) and in the winter the panels will block the wind. (The side facing the wall across the way will always be open hardware cloth for ventilation).
If it weren't for recent events (something breaking into my run and going after my chickens) I think I'd be happy to let them keep just doing their thing.
