Now on to the good practical projects. Research the use and characteristics of the items you are making. Buy from a known outdoor supplier. There are a bunch represented on the forums. Follow their recommendations and pay attention to the purchase. You want known fabric for top quality products. After a while, you will get to the point where you can go into the Wally World bargain bins and say to yourself "This looks like it would do." But even then, if I was building something I really wanted to be top knotch, I would buy only known fabrics from known sources.