Honestly, im not sure how to answer. On one hand, you should let them choose, but on the other, they can be a bit confused sometimes. Example: Its pouring rain, they don’t run into the warm coop with food and water, nor the covered safe run, they run under the wooden stairs, where theres a puddle of dirt they are sitting in. Or they run under the basement window overhang that requires them to balance as if they were on a tight rope.
But, either way, its their fault if they don’t want proper coverage.
Still, you could let them make the choice and see how it goes, they might not use it though given an option, because mine associate it with “bed time”
I figure that if mine *really* need significant shelter they'll make sure of such shelter since it is available.
Honestly, since they are livestock for me rather than lap pets, if they're so stupid that they do manage to do themselves an injury by not reacting appropriately to normal weather I don't need them in my breeding program.
That probably sounds harsh, but I don't want any weak birds in my flock.
That said, the last cold snap, where it suddenly plunged down to 20F lows from highs in the 70's, I had 6-week chicks newly off heat in the coop. They were fine.
