Buying a tarp...
Are you car camping...then weight is not a problem
....go with the bigggest cheapest tarp you can find
Are you backpacking....then weight is an issue
....silnylon is the best bang for the buck
....cuben is the most $$$$ but weighs the least.
Can you sew...then check out plans for a Black cat tarp and make your own
I own 5 tarps right know, each one gets used depending on the time of year and weather. I am taking a sewing class (with the wife) at the local community college to learn how to use my (our) thread injector so I can try making some of my gear.