Newbie questions -
Why does chicken roost? Why do they have to roost? What happens to hens that doesn't roost?
They roost because it is in their nature. From my limited understanding - they roost at night for safety. They tend to find the highest point they can reach to sleep so they are off the ground and away from the nocturnal predators that they would be defenseless against. At night and early dawn chickens are very vulnerable bordering on helpless when it comes to predators, poor vision and seem almost sedated.
I have yet to have a hen that simply didn't roost by choice. Young chickens and brooding chickens will not roost, and chickens that are lowest on the pecking order without a safe spot to roost may not either but generally speaking they all find a place.