Brian Liloia documented his build of this unusual round roof in 2008, while living in Missouri. This type of self-supporting structure, in which each beam bears the weight of another, and has its weight born by yet another, and all arranged such the load is thus distributed ’round in a continuous cycle, is called a reciprocal frame. It requires at least three members, and you can build a simple working model with matchsticks. [via No Tech Magazine]