I was playing around with Google Sketchup and did this 12 x 10 tarp design. It has no center ridgeline and only uses 7 yards of fabric rather than 8. The seams are 2.5' off the center line of the tarp.
Still learning about Sketchup, but it is a pretty nice 3D drawing program. Hard to read some of the dimension figures. The cat cuts are 5".