I'm working on a project in which part of the story takes place on a planet that is mostly ocean. There is a small continent with some manufacturing and refinery structures, but the rest of the planet's inhabitable area is composed of "floorscrapers." These are like high-rise buildings, but they are tethered together by bridges and float on the ocean surface. Each floorscraper rises only a few feet out of the water, with the building's entire "height" submerged in the water. The buildings have buoys around their top surfaces, and ballasts in the bottom-most sections.
In my story, these floorscrapers are the occupied space on this planet, and contain housing, recreation areas, commercial areas -- everything except the potentially toxic and polluting industrial business that takes place on the natural ground. As it stands, the lower down in a floorscraper a person lives, the lower their status.
I'm not familiar with construction and the effects of water pressure -- what facts of architecture would be different say, 90 or 100 feet deep into the ocean, within a tower-like structure? The inhabitants of this planet are humans with typical abilities, with similar mechanical advances to our own.
UPDATE: Following some very insightful questions, I think it makes sense to have all manufacturing, public utilities, and "functional" aspects of the civilization exist on the land mass, with the floorscrapers serving as hybrid living and commercial areas. The planet is a popular trade port, and little-to-no agriculture or industry outside of raw materials processing takes place on the planet.