it all depends on your regions climate, your exposure and airflow. my shed has decent air flow at the edges of the corrugated metal and timber construction. my exposure and height of trees gives me a lot if shade and in winter will get an hour or two of direct sunlight. in the summer there are shade trees and a heatwave is about 80 so for me baking them in their coop is less than likely.
given the number I have if they were to be coop chickens I would provide a larger ventilation . However they will be free ranging and will not be spending much of the day inside . Modifying my door to have a window and automatic door is in the works .
in in my experience with living things adequate airflow is essential for a healthy life.