Where I live in Southern Colorado, we have drastic temperature and weather changes. In my main coop, the eaves are open underneath, the main window opens, and I have two large vents, in the end of the roof peaks. The roof peak vents give me a total of about 168 square inches of ventilation on each end of the coop roof. These stay open year round. During the cold winter months, the eave vents are covered, but aren't air tight. The chicken access door stays open all the time except for very cold or blizzard conditions. At those times I close the chicken door until the weather warms a bit and snow isn't blowing into the coop. Remember that there is a difference between ventilation and drafty. You don't want a direct cold wind blowing on them while roosting, so design you coop ventilation with this in mind. The idea is to keep the air moving and not stagnant, but without a direct breeze on them. Consider the prevailing winds for your area and coop location when placing your vents.
In many warmer areas which don't get too cold, people used three sided coops for many many years without any adverse effects on the chickens and laying. The chickens just want somewhere to roost where they are safe and generally dry.