I live in zone 7/8 and I am planning on building a large greenhouse for winter planting. I am planning to make the south, east, and west walls entirely glass. The north wall I was going to make out of cinderblock.

I was planning on making the roof out of glass and at a 45 degree angle, but then I realized; in the winter the sun will never be directly overhead; and if I use the building in the summer, I will want to cut down on the daytime heat any way.

Should I make the roof glass or metal?