I have trouble myself doing those types of things, but maybe you could try starting with a box, and then, do some slice plane and cut (that will be in Max) not necessarily perfect perpendiculars. Then, select a good load of the polygons created by the cuts, and do some bevels. After you get a good load of them, and if you don't want rough edges rocks, do a mesh smooth. As I said, I'm no specialist in the matter, I wish I was, but if you're desperate try it. Most rock walls I've seen in games, are just made of textures and they don't look very good. Displacements may be a good solution, although I never managed to get what I wanted with them, when trying out for rock walls.