An Origamic Architecture (OA) is a folded sheet of perforated paper from which a three-dimensional structure "pops up" when it is opened. It is similar to a "pop-up story book", but its unique feature is that it is made purely by cutting a single piece of paper. Because of this limitation, designing an OA requires considerable experience. We propose a computerised method which assists design of OAs. An OA is modelled using a set of planar polygons. This model must satisfy the conditions required of a valid, realisable OA. A unique point of our method is the application of boolean set operations to the polygons on the unfolded pattern to guarantee that the model can be made from a single sheet of paper. We also present a procedure for checking the model?s validity. Additionally, we propose methods for creating openings, for generating unfolded patterns, and for displaying folding animation. We have implemented a system based on these methods and demonstrated its usefulness for creating OA. Our system allows designers to intuitively design OA models and to easily generate the unfolded patterns.