I used carved styrofoam insulation board as is pretty common now. The only thing I think make mine stand out from some that I've seen on other sites is that I didn't want them to look too new. I wanted the look of old, cracked and pitted. Like they had been forgotten in a run-down cemetery for ages. The painting was done in stages - a medium base coat followed by two coats, one light and one dark, applied with a sea sponge.
Waterfall with rocks. Rocks made with roofing paper and boxes. Waterfall made with styrofoam insulation sheet, light blue tablecloths from dollar tree, streamers from dollar tree and cello wrap for Easter baskets.