If your handy with a sewing machine you can make your own high specification Tarp exactly to your own requirements and design.

http://www.rockywoods.com/Fabrics-Hardwa...nd-UV-Treatment

An approx 10'x12' tarp material cost at $8.99/yard would cost $72 + shipping and weigh around 25oz or about 1lb 9oz. Using this rip stop material the tarp would be a lot stronger and more durable than any lightweight polypropylene tarp.

Goretex 3 layer ripstop can also be used but is heavier and twice the cost but because the material is breathable can be used as an improvised ground sheet bivi or blanket or even as a single layer enclosed tarptent design.

http://www.rockywoods.com/Fabrics-Hardwa...n-Charcoal-Grey

Were the REI polytaps ripstop and UV protected materials.