I'm going for big. I have the Hennessy Hex. It is PU coated and heavy (23oz). The silnylon version is 5oz less. A big Cuben cat tarp would be great. The Hex rainfly is 144" on centerline x 120" wide hexagonal-- I can have my own circus (at least the clowns).
You can always go to the hardware store and buy a cheap 12x10 poly tarp to experiment with-- cheaper is usually lighter. We're talking under $10 at Fred Meyer. They had some that are green on one side and brown on the other--- better than those [[[[[[blue]]]]]]]] things.