"Custom Shower" could mean a lot of things.
As far as the wall and floor, proper techniques and materials to make it waterproof are critical. Consult the tile forum: www.johnbridge.com
As far as the valves, you need to decide what you want. If you are talking multiple heads, etc. you need to consult the manufacturers specs as far as loop piping, and get a good plumber to determine what water supply piping will be required to feed your sytem.
Any plumbing showroom, or a box store, will have catalogs showing available suites. Also. go to any internet site (Delta, Kohler, Amer. Std, etc) for ideas.