I haven't painted PVC, although I've used it to make gates for our pony's fences. I've seen many examples of painted pvc, in trellises and other projects. Mostly I just wanted to add my own 'bless you' to concretenprimroses and grannytoo for your efforts to help the homeless. Worthy efforts indeed!

I'll tell you what I'd do, and remind you and myself that it is MikeIL that got me started in this business just a few years back. I now know enough that I don't always agree with Mike, but Mike knows and probably always will know more than I about building a variety of ponds. 25' by 35' is a big pond, at six feet maximum depth it makes me wonder what it is for if not for fish. Taking an occasional swim in it might be fun, but probably isn't the best of ideas if there are fish in there. Certain bacteria the fish are able to tolerate have killed a few humans (perhaps immunocompromised ones, but nevertheless it isn't a comforting situation). Because this size pond would be excellent for fish, I'd make it so it could have fish. If you don't place fish in it, fine, but you will have the option. I'd remind you that fish make quite a nice combination with plants insofar as you fertilize the plants every time you feed the fish. I would design it to take two bottom drains, not because that is fully sufficient but because that will be nearly adequate and won't necessitate still more pumps. I'd shape it to have two bowls toward each end and constrict its width in the center. That gives you easier access to the pond from the sides and directs the flow pattern well. 25' wide strikes me as a bit too wide to service easily with a net (either for fish or for leaves) and I'd probably shrink that a little. Where the two bowls converge I'd make it a bit shallower, directing bottom slope to each BD at the bottom of each bowl. I'd use two BD plumbed to a single settling chamber. Separate SC are better, but I like the simplicity of one. I'd dig an in-ground SC, around 1000 gallons, and surrounded by a concrete collar. On the collar I'd place a set of pipes to hold up emergent plants such as red stem thalia, rice, elephant ears, etc. The SC would feed to one or two pumps through one or two chambers filled with brushes. I'd use at least 4 TPRs to direct the flow in the main pond, clockwise in one end and counterclockwise in the other end. This will help direct debris to the BD. Since there will be a surface flow across the center of the pond I'd put the skimmer in the center of the long side where that flow intersects. It will help if that side is also that which prevailing winds also blow against, but it isn't mandatory. I think you're looking for more flow than is necessary for this size pond, particularly one that contains few fish. Circulating the entire pond volume in 2 hours will be acceptable IMHO. I think even the 1/3 hp pumps are uncessesarily large. I'd try to design it so I could get by with 2 or 3 low-head pumps, though a 5' lift is getting towards their upper limit for efficiency. I'd feed my TPRs via gravity from one of the bogs (presumably gravel veggie filters) so as not to waste any pump flow. The general design I outlined above is for a main pond primarily for fish and which feeds auxiliary ponds designed for plants. I like that plan because the fish, some of which can be rather nasty herbivores, are segregated from most or all of the plants. Since your vision probably differs, a different flow pattern may be desired. But you ask what I would do.

My experience is that PVC fittings break. PVC pipe bends in ways you don't want it to bend. If you're determined to use PVC anyway, study how metal pipe frame greenhouses are built and try to do something similar on a smaller scale. Make bracing connections to more PVC (or wood) using metal plumbers' strap and nuts and bolts. This will allow more flexibility in the joints. I've got plenty of broken pipe and twisted carriage bolts to show what a direct bolt hole through the pipe will do. If you have to put a bolt through, glue in wooden plug reinforcements to drill through. If you're going to sleeve PVC over rebar, sleeve a smaller bit of PVC (longer than the rebar stub) inside first to reinforce and spread the load at the pressure point. If you want advice on your build, post pictures of what you have in mind. It's hard to envision exactly what your structure will look like from just "a PVC greenhouse". Tell us about size and height. Tell us about shape (gothic arch, gable, round arch, low arch on kneewalls like Jay Slick's, etc). Tell us about frame spacing and what you'll have for purlins. I personally like wooden strapping and wood block gothic arch frames. They're easy to build, cheap, shaped to shed snow and wind, and they're very strong. You can fasten to it easily. In my limited experience, PVC is only suitable for very small houses, or for houses that will be disassembled and moved periodically on the shoulder seasons and left uncovered (no snow/wind loads) in the winter. Here is a link that might be useful: Gardening The Hard Way

The J channel is used to hide the exposed ends of the siding, you can't get around using J channel with vinyl siding whether it's vinyl or incorporated in the window wraps...find a local building supply store (not a box store) and get references to help find a contractor, because whoever is giving you these quoTes and "info" are way off. As far as the one piece window flashing what I've seen is a four piece system with molded corners and the only way that works is if they are gonna pull all the windows