[Context and motivation] In recent years, the Internet has led to new ways of doing business and spawned new business models. [Question/problem] Many business models have a platform orientation. For example, Uber and Airbnb offer platforms that enable broker/mediation services between parties organized in two-sided markets. Platform-specific revenue models are required to capture value from these intermediation services. However, it is largely unknown how to continuously design business models for a platform utilizing best practices. [Principal ideas/results] We propose three research directions to support platform design: (1) a classification of known platform business models, (2) a formalization of platform-specific revenue models into patterns, and (3) support for the dynamics of the platform business model, e.g., how platform revenue models evolve over time. [Contribution] In the long term, we propose a novel and tractable approach called the Business Model Construction Kit for platform business models. The kit will provide a variety of methodologically well-integrated design-oriented tools and accepted knowledge to quickly (re)design a platform business model with a focus on revenue models. The result is a method aimed at helping practitioners design platform business models.