I made my first rain fly from the material I got from Wally world. Turned out nice as long as you do not look close at the stitching that stuff is hard to sew!
anyway it is 11'6" across the ridge line. 12' d ring to d ring.
Info for you guys, I sewed it up first and then hung it nice and tight outside and applied the thinned out silicon with a paint roller. This was MUCH EASIER than doing the bucket dipping method that I tried as well. My thought also are that when it is hung taunt the material will open up between thread as it will be hanging and this is a better time to plug up the microscopic holes when it it is in its intended hanging shape.
Trick is to thin the material just right. thinner is better than too thick as you can go over it twice if needed but once it is too thick you end up with material that feels like wax paper.
Another piece of advice, when thinning do not dump a lot of thinner in at once, Just a small amount, stir rapid, add more, stir ect. Reason is you will not get a lot of floating thick chucks that will not get dissolved. once you get it thinned a bit you can add a higher amount at once but the first few thinner addings should be kept light so you can work it in good without separation. Hope this helps!
had the tarp outside in a rain last night and crawled under it this AM and the ground was dry and no drips inside. Now doing a sprinkler barrage as you can see in the photo.