The chances are that you don’t want to build your own submarine although this Chinese guy did it.
The better alternative is to get one of these personal submarines with 360 degree clear-view glass.
Now, someone reserve me one, I will pay you after you ship it to me. :p
They have developed a sub for 2 people. Called the Triton 1000, it is lightweight, and can function as an additional feature to your existing yacht. You can just go ahead and deploy the sub from your medium-large yacht. If you still don’t own a yacht, you can attach the sub behind a truck or a SUV and just negate the need to buy a yacht. With excellent visibility and luxurious interiors, the pilot of the sub will have a very comfortable journey under the water. The submarine is built specifically for the enjoyment of piloting one and hence the operations are easy. At about $1.69 million, Triton 1000 may be a little too heavy on the pockets, but you can do what no other yacht owner can do, view corals and the amazing underwater life or just have a romantic sub-ride with your partner.