I never liked folding/rolling my shelter, even when I *gulp* slept on the ground. My reasoning was the same as for a sleeping bag or quilt - if you start folding a piece of material, you'll tend to do it the same way every time. After a while, the creases will develop weak spots in the material and wear the item out quicker. So the sack is designed to just stuff your hammock/quilt(s). Unhook one side of your suspension, stuff toward the other end, then unhook the other side. The whole thing stays off the ground completely and thus dry and safe.
I haven't put my tarp in the same storage area as my hammock since the second time (give or take) I hung on the trail. Doing so just seems ridiculous to me - why would you want a (often) wet tarp in the same water-resistant storage as your hammock, which needs to stay dry? My tarp goes in snakeskins at the moment, but I'm working on a small BB sack for it, too. Not sure which I'll like better.
My current sack design is round-bottomed rather than square. The bottom is about 10" diameter and the sack is about 16" long when stuffed. That's after sewing, of course.