In 1979 the Swedish Housing Minister, Birgit Friggebo, changed the building codes to exempt structures under 15 square meters (about 150 square feet) from the requirement for a building permit. For this act, she has been immortalized, as these small buildings are now known as Friggeboden. There is some very interesting architecture being done in this market, including these designs from Sommarnöjen,, (Google translates that as Summer Fun) which hires some of Scandinavia's best architects to design them.
Kjellander + Sjöberg designed the Karlsson, "characterized by its open, bright rooms and glass, forming a whole with balcony. By a staircase at the back you reach the spacious rooftop terrace."
There are a number of available plans, but as this one shows, you can get a lot into 150 square feet.
Some of the other designs are quite attractive as well. But what is most interesting is how changes in regulations can cause such an explosion in innovation. In North America, many municipalities exempt buildings under 100 square feet from zoning regulations, but it is not consistent, and often the building inspectors object to their use as home offices. Perhaps we need a politician who wants to be immortalized as a building type here as well.