If you're interested in going the DIY route, you can use 3 yards of XL silpoly from Ripstop by the Roll, or Xenon wide from Dutchware Gear, and you can make a diamond tarp very easily. I've made 2 so far. Because you're making a rectangle (9'x6') It will be asymetrical when you hang it from opposite corners, but it'll have an 11' ridgeline for you and plenty of coverage.
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Here's the thread on how to build it with more pictures. Pretty much all you do is hem the 4 sides and sew on your tie outs.