Greenhouse attached to house: roof material?

Hello dear permies community,
It's good to be here tonight.
So.
I'm in the process of building a 9ft by 30ft greenhouse attached to the front of the house. I was able to acquire 16 glass doors from an apartment building for cheap for the walls.
But.
I'm confused as of what to use for the roof. I was thinking plexiglass, but it's 120$ for one sheet of 4ftx8ft. That's *way* out of my budget.
I guess I could do it with a bunch of ugly tossed out windows. But I was pretty happy of the uniform front with beautiful glass windows...
Any idea?
Thanks!
Tinkerig-Charles

Twin-walled polycarbonate panels or Solexx panels(merits discussed here: https://permies.com/t/44837/greenhouses/Solexx-Polycarbonate) would be a couple options. Neither cheap, but cheaper than plexi. Corrugated single-wall polycarbonate panels are the cheapest option I know of, but not as aesthetically pleasing or insulating.

Something to consider is whether the entire roof needs to be transparent. Depending on where you are, and the direction the greenhouse faces, and the slope of the roof... the portion of the greenhouse roof nearest the house might not be necessary to have transparent; much of the year it may not occlude light from reaching the plants. Whether you need the heat gain from that sunlight hitting the wall is another question...

I am considering vinyl. Clear, cheap, but it would need considerably more support.