Not sure exactly what you have in mind, but here is one slightly unusual technique:
There is an old-school technique for making sedimentary cliff-faces that involves stacking broken pieces of ceiling tiles. The rocks in this scene were done that way:
BUT, it is also possible to create flats by cutting and stacking very thin strips of tile and hot-glueing them together:
You can also carve the back surface of a vertically-mounted piece of tile. The face in the rear of this scene was done that way:
A Dremel tool is good for doing the carving.