To understand a little more about how condominium ownership works, relate it to owning one piece of a pie. Everyone who owns a piece, shares ownership of the single pie plate and responsibility for its maintenance and upkeep. The cost of maintenance is divided among all the pie owners based on the day to day costs and reserve costs, or money set aside for future repairs.
It is not a new thing to share and sell part of your home. Colonial mansions in the older areas of the USA have long been divided and sold. It is also a very popular feature of British real estate, and the most common way for first time buyers to get their foot on the property ladder.