50% mesh will provide a large wind load. That assumes 50% open area and 50% netting material. I've tried similar with 30% hail netting. The wind load was more than I expected. And 15ft is pretty tall. You better have a strong frame if your winds ever exceed 30-40 mph.

I agree with fruitnut.

Gray PVC is electrical conduit. Get the kind with belled ends so that it glues together without fittings. Try to get schedule 80 instead of schedule 40 as it's much stronger. You will want several purlins in addition to the top purlin. The good news is that you don't have to worry about rain pooling on your plastic roof, due to it being netting. Attaching the purlins is easy if you use duct tape, but it will need to be re-taped every year. There are other vinyl tapes that would probably last longer in the sun. You can re-enforce the purlin connection with cable ties, but once again the plastic ones don't last very long in the sun. Metal ties might be worth the money.

Anchor your end hoops well. You can use guide wires if you have something to attach them to. If you're in a tropical area, you could also plan to remove your mesh cover in the event of a hurricane or tropical storm.

Thanks.

We get strong winds at night but no hurricanes (Panama is too far south). Prevailing winds will come from the end of the building-plans are to put a concrete building on that end. Should be able to anchor my first hoop to that.

Am planning on using 3 purlins with steel clamps around the hoops and screwed onto the purlin at each intersection.

I'm thinking of securing the mesh to the hoops (4 ft. spacing) with about a million zip ties.

Plastic zip ties will disintegrate in the sun very quickly. I've given up on using them outside. Some sort of vinyl-coated wire would last longer, like a heavy-duty twist tie. You could also make your own clamps out of pipe cut in half long-ways.

I did a bit of research and found UV resistant zipties. They're called Tefzel made from something called ETFE.

Update on that last post: Did a search for "UV resistant cable ties" and found ones that are much less expensive then Tefzel. They are just nylon that have been treated, rather than a high tech material. Jon