A couple of weeks ago I came across a comment on TMP about molds for some scenics, and it directed me to here. So I picked up mold #93 from this page. Lovely sloped walls - could almost be Chinese! I've started making lots of "bricks" (or rather massive blocks) to make some Martian city walls. The process is a bit fiddly, but I get to revert to childhood and be a bricklayer / lego builder again.
I'll probably make them 3 blocks high to start with (that's 1.5" in old money) plus a parapet (the lotus-pattern bricks with an outward curve). That should be plenty for a provincial town or outpost.
It will probably need a pretty rigid base as I don't think they'll take happily to flexing, but we'll see where it takes me.
If anyone out there has some tips or tricks with using plaster of paris for builds, please let me know!