The current marketplace can be characterized by the need for variety, faster time to market, and decrease in cost. To survive companies are shifting from a mass production mode to mass customization to provide the necessary variety. One of the key elements of mass customization is the product platform. In this paper we will investigate the use of graph grammars to develop common platforms for a set of similar products and to specify the product portfolio supported by the platform. To facilitate development of common platforms a formal product family architecture representation is presented which separates the core and the options to facilitate the identification of the common platform. Graphs are used to represent the core for function and structure viewpoints, and grammars to specify the relationships among the core and the options. Arguments on suitability of graph grammars in common platform development, are also presented in the paper.