I love it, that is a great idea. I can imagine how cool it will look with the sharks swimming right above the sand bottom in and out of rocks, 2 cool! Word to the wise, 2 years ago I bought my dream 180 Oceanic tank, spent 2 weeks making the custom oak base and canopy then spent the next 3 months setting up and cycling the tank. after 6 months I had what I always wanted a beautiful SW aqu. with the fish I loved to look at. But then I slowly realized that I was spending more money on water changes, buffers, filter cartridges, carbon, food, ect. than I was on my new truck. That does not include the the time I set aside each day for maintance. After I cried like a 2 year old I sold my dream tank and contents. Now I am setting up a 55 gal.
Just keep in mind the cost, and if you feel you can do it, then set it up and post some pics. so I can drool and dream.