Same But Different Department:
I strung heavy clear plastic sheeting over my clotheslines last year, in a Very Failed attempt to make a bit of a greenhouse for my more delicate outdoor plants. We don't get snow where I am, but we do get the occasional rain storm, which can dump a serious amount of water. The tarp held, with a good 10 gallons of water in it. It bent the T-poles for the laundry lines..... Not badly, but it's noticeable if you stand in the right place. Nor did it save my plants, incidentally, but that's a whole 'nother story!
You need serious support under the tarp, and to pull it snug with ties or bungees or some such, so there's no sagging areas to collect debris, snow, etc. One of the reasons actual, official, greenhouses work is because they're rigid, and there's a limit to how much of anything can collect on top of them.
