The availability of reference models for data warehouses lowers the obstacles that inhibit small and medium-sized enterprises (SMEs) from using business intelligence technology. Service providers may offer to companies a set of pre-configured reference models for various industries. Modelers may then customize the chosen reference model, tailoring the model to the specific needs of the individual company. This customization may consist of additions, omissions, and modifications with respect to the reference model. In this paper, we propose a metamodel and customization approach for reference multidimensional models. We emphasize simplicity and understandability in order to facilitate the introduction of business intelligence solutions in SMEs. Furthermore, we specifically address the explicit modeling of key performance indicators and their calculation rules as well as the definition of reference data marts for report building.