As the days get shorter, your chickens will spend more time inside. It’s important to keep fresh water and feed available. In cold weather, there’s a temptation to close all the doors and windows to keep them warm, but they really need fresh air and adequate ventilation.
One approach that can work well is the deep bedding or deep litter system. Basically, you keep a thick layer of high carbon bedding, 8″ or deeper on the floor. This can be dried leaves, sawdust or wood shavings or other similar material.
As your chickens drop manure on the bedding and turn it by scratching, the bedding will turn into a living compost pile inside the coop. It will have a clean, earthy smell, and will be quite sanitary. If you start to notice an ammonia smell, then it needs more carbon material added to the bedding. Also, make sure that it doesn’t get too wet. It can tolerate some dampness, but you don’t want it soaking wet.