With Ocean Atlantis, construction plans should start out with creating a work station. A volunteer builds a home on the floor of the ocean, and sets their home warp there, so that others can use it as a gateway into the work-zone.

Build a base ring for the dome around or near the house and slowly build a dome, temple style (layer by layer), and then hollow out the dome. After the first dome is made, make the tunnels out for the other domes and then repeat the process, the other domes will be easier as we can make the domes at the end of each tunnel.

But I think the idea of having multiple entrances to the city could be troubling since unexpected guests can jump in, and securing each entrance can be gaudy. So I will draw up some of my ideas for the entrance, and some ideas for the city layout.

In another post by Zen00, he explains that he and an admin friend used /butcher command that removed all the hostiles on the map, so the cap got cleared and now they are spawning more frequently as of late.

There are two methods to create the Atlantis Project in the new map, Ocean or Aquarium.

Ocean Atlantis
 The positive attributes for this style would be it's authenticity to the original mythological city, sans massive sinking into the water part. The borders of the project would be more open, allowing the expansion of the city to be more fluid. The city would be isolated and less probability of griefers stumbling upon the area.

 The most negative quality of this style would be the construction phase, since builders would need to litter the floor with breathing stations to make it easier for them. Also the roof cap of all buildings would need to be very restrictive if its going to be completely submerged which can stifle creativity. Then there's the problem that other players can create other structures over the city, on the water or over it.

The way to overcome the roof cap would be to dig downwards in the building to make more floors and have underground tunnels leading to other projects. But from what i have read the plan is to make underwater domes that cover the area, which has it's own negative qualities since the buildings would need to be centered or small and to make them the area needs to be drained, built, then reflooded.

Aquarium Style

 The positive qualities of this style of construction would be that the city becomes quite a spectacle for all to see, revealing the scale of the city. The construction phase would be easier as we can work on dry land, then flood the city  section by section. The height cap is only limited by skylimit, and the construction of domes can be made easier.

  But it's negative qualities of it is the amount of materials needed to make the tank itself, since glass would be most appropriate material for the walls of the tank and to flood the area you would need to construct a shelf at the very top which could be dangerous work. 

Well it seems that there is an alternative method to building it. we can build an aquarium style Atlantis, where we make a big fish tank; level out the area, replace the floor with sand, then construct a glass case around the area. to flood the area just make a dirt shelf at the very top that covers the area then place water on the shelf, break the shelf then viola instant atlantis. It would be more of a spectacle as well, since everyone can see the magnitude of the city. We connect the buildings with glass tunnels and the entrance of the city will be made of an iron block double door that opens up with sticky pistons. 

atd I can make you a proper 1hit kill spawner, but I would need 2 sticky pistons to get it to work, but if you can't get them I can just make a holding pen for them where people can kill them manually and to where they can't reach you.

spamarian you do know that a rollercoaster isn't supposed to be a straight line that sends you far away from the starting point, that's a railway. So my rollercoaster is long, just not long-distance

Actually if you hit the border when riding a boat it pushes you out of it and the boat floats outwards.

SO I guess I'll make an obstacle course instead.

Well I constantly find them floating around in the ocean and there are so many that just floated past the worlds edge.