This thesis explores the design and building of FlexM, a computational construction kit for building and manipulating 3D geometry for architects and designers. The purpose of FlexM is to put the control of modeling with the computer in the designer’s hands. FlexM is a design concept to be realized in this thesis. Using the FlexM components of hubs and struts in place of the standard keyboard and mouse, the designer can build a digital model with physical constructs. Architects are trained in the tradition of model building to develop spatial skills, to foster an appreciation for materiality, and to offer the intrinsic satisfaction of mastering craft. In addition, model building aids in working out 3D design details, and in visualizing the nature of architectural spaces. In spite of their precision and efficiency, conventional computer tools for the architect, like CAD (e.g. ArchiCad, AutoCad, or Microstation) or 3D graphics applications (e.g. FormZ, Maya, Rhino or Studio Max), strip away the essence of architecture - the joy of craft. Why can’t the designer interact with the computer with the freedom and ease of a toy? FlexM will bridge the gap between the physical, tactile interaction (play) and the computer interface. It aims to provide a versatile modeling interface between the designer and the computer.