Since we don't have a new thread, and someone suggested we make a plan, here's my idea:
We do the Rapture city everyone has been talking about. Buildings sit on a grid on the ocean floo, and cannot come within eight blocks of the surface. Apart from that there are no restrictions. I recommend we go for a unique art style, with buildings having designs that would not work on dry land (floating platforms, massive glass domes, etc.) There should als be underwater streets between the buildings, lit by glowstone lanterns and given park benches and such, plus a submarine dock.
One the surface there should be a floating tower connecting the residents of the city to the surface world. It is were all visitors have to pass through to enter. It should be tall,, with a beacon at the top (colored glass mod?) and be connected by an elevator or stairway to the bottom.
Beneath the city we have the slums. Thee are long, narrow, and dimly lit tunnels and apartments dug beneath the ocean floor and connected to the above by a few well-secured gates and a few holes to the open ocean. These slums should be large and hard to navigate. There should also be an underground stadium for public entertainment, a mine, and maybe a couple of secluded vaults and the like.
The city should be huge, though we don't have to give it the retro bioshock look. Futuristic is also nice.
So, what do you think?
Let's all agree on this theme.