The shape of the building is not something simple like a sphere, or an egg. It is something akin to a drop of water being blown over by a puff of air. Each level is offset slightly from the one below, hanging over one side of the building. The result is a slightly curving side, and a rapidly curving side. This is an energy-saving feature, as the building is angled to take advantage of sunlight in the winter, and avoid it in the summer. There is a below-grade ampitheatrer, which makes the building appear as if it is rising from a hole. This description was taken from the webpage linked here, where you can find more pictures of London City Hall.