Imagine a large donut. Now imagine that the donut is sliced in 12 wedges. Each wedge would be the size of a cruise ship. You could cpntract with a cruise ship manufacturer to assemble each wedge. Each wedge is a complete ship. It could function as a stand alone ship.
Each ship would attach to each other until the donut was complete. 12 cruise ship size pieces assembled into one city on the sea. 12 propulsion systems. If a wedge needed to be replaced it, you would order a new wedge and switch them out. The city could be constantly upgraded with new technologies. You could have multiple floating cities. If 2000 people lived on each wedge, thats 24000 people. If each person paid $100,000 for a spot, thats 2.4 billion dollors for construction.