There is much at the top - the roof is not air tight at all. Also, I don't close the ramp door ever as they're inside the pen. The bottom has screening as well. I may add more at the top but I've never seen them inside during the day as of yet. It also in the shade almost all day.
I agree you'll probably need more ventilation along the top near the roof, not just for ventilation, but also perhaps a couple of windows backed by 1/2" hardware mesh to allow the coop to cool off during warmer months.
I think @ilikechikin mentioned that he was upgrading the run to 4x4 posts and welded wire?The ventilation is to get ammonia laden air out of the coop while they roost. Chickens produce a ridiculous amount of poo at night. That produces a lot of ammonia and moisture that needs a way to escape, otherwise you will have ongoing respiratory issues and frostbitten combs in the winter. And that pen is just chicken wire and no cover. The door should be shut at night to keep any nighttime predators out.