I've been reading some other threads on the subject and it seems that plastic sheeting will degrade quickly. It's only to protect from winter rain.
My original idea was to have a roll-down roof, maybe just a tarp or canvas that would roll up neatly on top.
I would rather the roof be permanent though, clear plastic that would not filter out too much light. Any suggestions?

Have you already considered plastic greenhouse film, such as this product rated for 4 years of use? http://www.greenhousemegastore.com/product/4-year-greenhouse-film/plastic-greenhouse-film

You know, I did look at it but I was concerned I would be filtering out too much UV.
This greenhouse is for mesembs and a few others from seed.
I only want to block out 40% max. I read that the 6 mil greenhouse film blocks about 10%, so maybe I'll go with that plus a 30% shadecloth?

that is awesome. great work.

I use the 6mil generic and it lasts one season, the largest roll at Lowes or Home Depot will supply enough plastic for 4yrs on my 8x16 and 8x12 shelters. I've tried the greenhouse plastic and it lasts longer but I have to fold and store it every summer. I got about 3yrs out it.

Have you thought about using twin wall AKA poly gall on the roof. I am not sure about what its Uv rating is.

Great structure

I just wanted to update y'all on my greenhouse. I built these two tables yesterday. I have the plastic partially secured now and I'll try to finish covering with the shade cloth today. We've had a few non-windy days so I'm trying to knock this out.
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Been working on this all day. Should be totally done tomorrow. I used 6mil greenhouse plastic and 30% shade cloth in a 12' roll. Today I secured the plastic, tied the frame off to the tables, spent about 3 hrs making 10 PVC clips and then threw the shade cloth on. Tomorrow, I'll make the rest of my clips and finish the front and back.
I'm exhausted. :)
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PVC clip. You can see two of them on the bottom of the frame.
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Great job. Really looking nice. Lot of work going into that.

looking good. all that work will be worth it in the end, i am sure.

Nice neat job. PVC pipe is kind of like Tinkertoys. People build all sorts of things out of it.

Ryan,

That's looking great - imagine how much your plants will like it, too. Are you going to have to heat it, too, or are you using solar panels and water?

Thanks, everyone, for your encouragement. It has been a lot of work but I know it will be worth it. This is how I am... I find something I like and I go all the way with it.

Jeff,

I don't think I'll need to heat it. Here in Ventura it doesn't really ever frost. We have one of the most temperate climates on the planet. Maybe there's something I missed? but the gentleman at Mesa said I have ideal conditions for Mesembs, said he'd like to trade places in fact, and only recommended a roof to protect from winter rains and 40% shade. The plastic is 91% light transmission so I guess I have 39% shade.
Please fill me in if I have overlooked some crucial info.

Ryan, no, but I didn't know you lived in such a succulent-friendly area of CA. I didn't know what directions (plant-wise) you were growing, but some Euphorbs and such like warmth in the winter - they grow so much better with it, and you can keep pachycauls growing longer (but even Pachypodium namaquanum was out of leaf only two months a year in San Diego). I've never had a greenhouse (just an open-sided structure) but it might have been a concern depending on the plants you grow. Remind me, please, to have a heater installed in the greenhouse up here should I find the cashish I'd need. See, I knew someone would need one.

Ahahaha! Phew! (sigh of relief) It's a bit late in the game for me to make any big changes. I'm mainly growing Mesembs in it but also some Aloe, Ariocarpus, Bulbine, Gasteria, Haworthia, Huernia, Pseudolithos, Stapelia, and Avonia, all from seed. Many will eventually migrate out. At some point, I'll probably add a second shelf on the tables and grow Haws and other low light plants down there.
Knowing myself, I'll probably get really paranoid when it does start to get cold but, you know, "you gotta have faith." -George Michael

Hanzrobo, nice job, I hope all your plants will be happy this winter.
Marie

Ryan,

Wham! There it is - proof in the pudding. As I said, I've never had an actual greenhouse, but a number of experienced growers in San Diego had them, so there must be something to it. Maybe it wasn't so much about the heat as about being in total control (if the greenhouse was pollinator-controlled) of what plant crossed with what plant. As you know, there are year-around pollinators there (and probably where you're at, too) - hummingbirds, flies, bees, beetles and so on.

Thank you Marie. I hope my sophomore attempt at seedlings won't be a let-down.

Jeff,

I guess I'm going to have to cross the pollination bridge when I come to it. When the time comes I hope I can find ways to isolate the plants and keep my seeds thoroughbred.

I just received my 200 3.5" square plastic pots, the seeds are on their way and now I must concoct the perfect soil mix (God help me).
I've been trying to finish the shade cloth for the last few days and it's pretty much done. I had to sew on the front and back and around the door using plastic-coated wire, took forever, still not completely done. What's left to do after that is pretty much aesthetic besides the zipper door I'll be adding whenever I locate one.
Will someone remind me why I didn't buy one of those $200 ones that are the exact same size? Oh yeah... specifics.
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