Robots developed for social interaction and care show great promise as a tool to assist people. While the functionality and capability of such robots is crucial in their acceptance, the visual appearance should not be underestimated. Current designs of social robots typically can not be altered and remain the same throughout the life-cycle of the robot. Moreover, customization for different end-users is rarely taken into account and often alterations are strictly prohibited due to the closed-source designs of the manufacturer. The current trend of low-cost manufacturing (3D printing) and open-source technology, however, open new opportunities for third parties to be involved in the design process. In this work, we propose a development platform based on FreeCAD offering a parametric, modular and open-source design tool specifically aimed for robot heads. Designs can be generated by altering different features in the tool, which automatically re-configures the head. In addition, we present several design approaches that can be integrated in the design to achieve different functionality (face and skin aesthetics, component assembly), while still relying on 3D printing technology.