In order to provide products that can be tailored to the need of the customer, it is necessary to integrate the customer into the design process. In this paper we present a mass customization computer-aided design (CAD) framework that helps to integrate the customer into the design of user-configurable products. A template approach, which considers both modularity and scaling, is utilized to concisely represent a CAD model of the entire family. The system accepts user selections and parameters to automatically create a CAD model of the customized product in real time and then shows the model to the user. The system is implemented using PRO/ENGINEER and demonstrated through customization of bicycle frames.