I'll also point out that unless those windows are near-free it'll work out to be cheaper to buy a greenhouse kit. Grower's Supply will happily send you a lust-inducing catalog.
oh yeah, I'm building it because we just got new windows and those are the old ones they took out. 100% free. I am, however, trying to figure out the roof, which I'll have to buy, and this site looks great for that. I really want the steep side that face the sun to be able to lift for air flow, but that might be too much for this project.
My casual observations in no real order. They make actuators with a fluid that passively expands when it gets hot for greenhouse applications. Kind of pricey but really cool. Also think about the edges of the window, idk what yours look like are they channels or some other shape that will trap moisture and mold? You will want an upper beam thats not in the sketch on the roof, that will prevent the panels from taking a bunch of shear load. You are missing a window retention ledge i think, those windows will take a ton of load, you will want a strip of wood or something to distribute load into them. You probably have too many windows, you don't need that many since at least 1 side will very little sun. Figure out what the available angles are for metal roof brackets at the hardware stores. Use one of those if not using one already. The center span will sag way too much. Youll want to put posts every 24" or closer. 4 post wont cut it with that long of a span.