I have two coops that DH custom built for me. The main coop is 4x6 with 3 external nest boxes and no insulation but very solid construction. The design is a sloped roof, 5' high in front sloping to 4' in rear, & roof extends over nest boxes. All roof eaves are open, along with three windows with only hardware cloth. I only have 4 hens in there, 2 lav orps, 1 blrw & 1 americana. Not much body heat to keep the main coop warm so I covered each window in greenhouse plastic for the winter. The mini coop houses 4 silkies and it is 3x3 with a peak roof, and all eaves open. They have one large hardware cloth window. I use deep pine bedding in both coops. When the deep freeze hit us in Pa, I put a double layer of bubble wrap all on the windows. I tried several different ways of keeping the water from freezing, including using my heatmats for seedlings but they dont produce enough heat. the best solutions have been to swap out soda bottle nipple waterers every morning. I keep one hanging by the kitchen door and fill it with warm water in the morning and just swap it out with the frozen one in the coop. It stays defrosted all day but does freeze up over night. I left the heatmats in because the girls like to stand on them. I give them lots of treats and do not let them go outside when temps are below about 25 or wet, but otherwise they love running the yard especially the silkies, they love the snow! Ive gotten eggs all winter from most of the girls and only once or twice found a frozen egg. So, the cold does not really bother them one bit, even the sub zero wind chills. I did, however, just hatch out some new additions to the main coop in hopes of keeping them a bit warmer next winter - CCL, Rhodebar and the floppy combed brown leghorn, so we will see about frostbite next year...