As the title says this is my first go at an underwater project, I used single player command to help me construct the foundation and to supply most of the materials. It is a Bio Dome of sorts with four interconnecting circles that i shaped into a dome.

Had i known better i would have used MCedit probably to fill the 50x50x20 Cube and the same to dig it out. But that was the only way i knew to get rid of that much water in Minecraft.

Let me know what you think of it.