Making a rock garden is one of the most fun and creative forms of gardening. I recommend that on your first attempt, you try not to think too big. A giant hillside might be overwhelming for your first try. To really enjoy yourself and keep a cool head, I recommend you treat your new garden more like painted a jewel box egg than a reckless out-of-control rambling flowerbed.
Some homeowners design rock gardens to exploit rocky slopes that constitute problem areas in their yards. Others import rocks into yards that are flat and that lack rocks. In the latter case, stronger backs are required, but the effort is well worth it.