Answer: That's a pretty deep subject and there's not enough room in this format to do it justice so I'll have to direct you to outside sources. There are several how-to books available in your local garden center and tons of books available at your library. You can glean all kinds of ideas from these and then design your own once you decide how large, how deep, and how you want it to look. Most books have sketches and materials lists to help get you started. Good luck with your project!
Q&A Library Searching Tips