We love super-tiny prefab houses, from the Weehouse to the Tumbleweed House. The Loftcube is another classic prefab home, designed to make use of the extra space on top of city skyscrapers (and designed to weigh little enough to be delivered there via helicopter!).
The whole home is less than 400 square feet big, including the kitchen and bathroom. Still, with glass walls (available either with or without blinds) and sweeping views, it seems like it could feel much more spacious. It's not totally clear how it can be hooked up for plumbing and electricity. It's also not clear how environmentally-friendly the building materials are; other prefab homes are more on top of this. Still, with such tiny living quarters, you'll automatically have much less impact than in a regular house. And we love the idea of making use of rooftop real estate, or other unused spaces. Prices start at $139,000.