If you want a good source of light and warmth for your chickens during the cold months of the year and a solid source of ventilation during the hot months, then be sure to install the chicken coop windows facing the southside where they will receive direct sunlight throughout the day.
On another note, if your goal is to raise chickens that will produce great eggs all year round, then you should look into an electrical source of light. You should be able to easily install an electrical light at the height of the chicken coop's ceiling which will help keep your chickens warm and help them lay better chicken eggs throughout the year. One ceiling light should be enough for a small scale chicken coop, for larger chicken coops though, try to install one electrical ceiling light per every 30 - 40 feet.
