hey mate,
great to hear that you are getting ready to venture into the deep art of rockwall making!!!! Only kidding, it is pretty easy and fun, if you head over to the
DIY Zone there are some pretty cool tutorials/ideas/photos people have put up.
basically, you need foam (polystyrene packing foam), you then stick it to your enclosure wall, shape it into rough rocky shapes, then cover it with layers of tile grout or render, do about 5-6 layers of this (mainly because dragons chew) then paint it and seal it with a waterproof sealer. bassically bunnings will be your heaven for this kind of stuff.
anyway, take photos as you go and post them, and read up on some other peoples work before you start
josh
here are some pics of one of mine