The triangle under the roof is called gable vent. They are strategically located at the high point. Warmer air rises, carrying the moisture and vents out at the high point of the structure. So install them on both sides with shutters so you can control it according to the weather. However, there must be make-up air from a lower point so you wont create a negative pressure in the cabin. In my case, my pop door is open to provide the make-up air.