Whichever the type of housing you choose, ventilation is important. Ventilation should be well above the highest roosting point, rain and snow free and the coop kept draft, rain and wind proof. Proper ventilation will avoid a high level of humidity in the coop.
Poultry can resist cold temperatures to a certain degree and according to breed. Heavier and dual purpose birds do better in cold climates than most. It is advisable to keep the temperature in the coop above 40°F. Birds puffed up, shivering and standing on one leg is a sign that they are suffering from the cold. See the medical section concerning frostbite.
Coop friendly flat panel heaters exist and are a safer option to heat lamps which can be the source of fire and are expensive to run.
Extreme temperature changes between the inside of the coop and exterior should be avoided.
In high temperatures, if the ventilation is insufficient, it can be improved by installing a fan to circulate the air.