I recently broke ground on a new base. Gonna be out in the middle of the water. 4 massive towers connected by walkways, set on wooden platforms with support structure going down to the sea floor. Possibly going to have farmland on the roofs, and some kind of central structure.
The plans I drew made it look like a Companion Cube from the top.
I wanted to make it out of brick, but my calculations indicated that it would be prohibitively time consuming to gather enough clay, so stone it is.
Basically, 4 of these [http://www.majhost.com/gallery/lakonua/Minecraft/tailii_tower1.png], a few floors taller, with wooden walkways between them.
Huge, awesome, and complicated. My kind of project.