Hello, I am new and in zone 7b not far from zone 8, our summers are long, humid, and hot. However, we get hard freezes and a handful of 20s nights in the winter; rarely it gets colder. During the summers I grow tomatoes and peppers in pots. I enjoy growing my own food so on a bit of an impulse I bought a Day Avocado tree and Dwarf Orinoco Banana tree. They should do well in pots outside during summer but will need warmth during winter.

My breakfast nook is south facing with 6-8 hours of sun during the winter time. It is a perfect spot, but.... I was would like to get a Bearss Lime tree, Arbequina Olive tree, and plan on trying to grow a Dragon Fruit cactus from seed. The breakfast nook isn't near big enough plus I am not a big fan of house plants and having a cat doesn't help. My options as I see them:

Turn my ratty back patio into a lean-to greenhouse; my preferred choice so I can harvest year round. The house would be approximately 12' x 18'-20'. The aluminum kits are too much but I have the skill and knowhow to design and build it myself. Before, I delve into various issues, I have one question that may be the deciding factor.

How clear is clear double wall polycarbonate?

It is hard to tell from online pictures because I suspect most of them are of the glass house options. I'd rather not obstruct the view from my living room of my cottage garden I am working to cultivate.

If I can't make the greenhouse idea work the only other viable option I have is to accept that I can't grow year round and overwinter everything in my garage. I am currently attempting to overwinter some peppers. I'll know if they make it in a few weeks but I do know it got close to freezing if not right around it, I had conflicting temps from thermometers. I can get the garage temps up by replacing the current insulated door which has serious air gaps with a new properly aligned one, My parents' garage with an insulated door stays at about 55 during the winter with temps not less than 45 on the rare, really cold nights. I can also work out some reliable supplemental heating as needed.

The big question is can the things I am interested in growing survive over winter with those temps and the light from the north facing garage door windows?