Greenhouses are such an individual thing. Seed starters VS a constant use GH, what you grow, when you want to grow it, where you are make it -a living breathing thing really. Ventilation always seems necessary and it is good to be able to vary the amount due to heat and humidity. Shade cloths on the windows should be at least thought of to keep temps down. A fun journey and good thing is you don't have to create the perfect thing all at once. We did roof top poly vents. Built a frame, curbed it so it wouldn't leak. Added the little automatic vent openers. In the end, something else simple we did made all that unnecessary. Have fun.