I'm new to this forum, and have some questions. We're in Iowa, zone 5. So far I'm planning to build the greenhouse from used patio doors, primarily. I have enough of them. They are essentially a large window, consistently sized, at least 1/4 inch tempered glass. Do you think this is a good idea to use
the patio doors? I am also considering using them for the roof, at a 45 degree angle. Of course we can get hail, it isn't common, and usually not large
hail. I am optimistic the tempered glass, at that angle, would stand up fairly well to hail. I would design it so that replacing a broken roof panel would not be too difficult. I am also thinking that at the 45 degree angle, I could add glazing to the bottom of the roof "sections", so they wouldn't hold any rain/water there. Another thought/question.....would we be just as well off to have the north wall solid or mostly solid? If not having much glass in the north wall is a good idea, I would probably like to put in some glass just for visibility. I will probably not put in a heat source just yet, and see how it goes this winter. I am planning the size to be 8' X 15' so that we don't have to deal with a permit, inspection, etc. I plan to install some type of temperature
regulated vent/fan also....probably initially powered by a couple solar panels if that is workable....as of now there isn't electricity to that area. I appreciate your thoughts, suggestions. Thanks! Gary

I'm a big fan of using found stuff. My own greenhouse is covered in salvaged floor protectors, those super tough clear plastic things under desk chairs.

Depending on the design, you might be able to drill small holes in the down end of the frames to drain water. I like all sides glazed, but there are plenty of lean-to and such greenhouses against solid walls. If it simplifies your design, you can consider a roof with a single south-facing pitch. Here's a little site with stuff on roof pitch with regard to winter solstice sun angle, glazing materials, etc.
https://ceresgs.com/whats-the-...

You can do somethings to help the warmth. A masonry floor, like concrete pavers, will hold heat from the day. Some people hang temporary bubble wrap. I've not done that, my winters aren't bad enough for long enough, so I don't know how it works. I'm redoing mine, and I'll have some shelves using some of those blue plastic drums you see offered on Craislist as supports. They'll be full of water, and that mass of water can hold a lot of heat overnight. It's passive and won't do any harm over summer. And like the house attention to sealing well, both by design and by treatment, makes a big difference.

See what the temperature does in summer to know if you need anything more than passive ventilation. But where winters are hard, vents need to seal up pretty well, even using inserts, like storm window treatment. Vents are most efficient for cooling when located at the peak, although if local wind conditions are steady, cross-ventilation is valuable.

Thanks Gerald! I checked out that link, some good info on there. I like the idea of concrete pavers, I had been thinking of a gravel path down the center. I also like the idea of the water barrells, I'm planning on doing both of these.

Gravel works, too. You just want some rock. But one of the advantages of pavers (if you're up for some extra work) is that, if you can manage to insulate them from the ground, they will put their heat into the house air, rather than into the ground.

Admittedly, I've never carried out that scheme, since I hardly have that kind of cold problem. But one approach is to build a wooden floor slightly above the earth and lay the pavers on top of that. Another one that's easier but probably not cheaper is to lay a layer of perlite. Or packing peanuts, if you had free access to a bunch. Anything full of air that won't rot. And what I find attractive is 4'x8'x0.5" insulating board, about $10 at Lowes. The 2'x8'x2" expanded polystyrene is about twice as much but is rated R-10 and rated for sub-grade. Both add just a fraction of the paver cost to the project.

You may still need some sand to level a base for the board.