Did a little experimenting this afternoon with cheap vinyl floor covering material.
Pros:
* Measures 18.5 inches thick in Z scale
* Better natural color than Linoleum
* Self-adhesive for quick assembly
Cons:
* The printed surface is white when cut, and must be carefully trimmed to minimize its appearance
* The surface is not true, and each course of stones must be sanded flat before applying the next course
I cut a strip three scale feet wide. Like Chris I sanded the sides of the strip before cutting the stones so they would pack together tightly. I also took the extra step of beveling the edges of each stone face to better mimic the real thing (
http://nebrownstone.com/images/Gallery/abutment2.jpg), which slowed down assembly--however, being self-stick made up for it.
The choice of the color/pattern makes no difference, since it's not seen; what matters is the color of the material itself as well as the surface texture--I couldn't find one that was completely smooth, but some were way more textured than others, so I chose the smoothest one I could find. The material beneath the thin printed surface has a nice natural medium grey.

Here's three courses assembled.


I stained the surface with a light India ink wash, then posed it with some figures for size reference.

Overall I really like this material. I could see myself cutting many hundreds of these stones over the coming weeks/months/whatever.