The absence of software support for early-stage design suggests that conventional graphical user interfaces are inadequate for this task. Perceptual interaction -- in particular, pen-based interaction -- may afford more natural and intuitive user interfaces for design support. The development of a multimodal intelligent design studio poses several important research challenges. Natural multimodal interaction demands a better understanding of how designers use sketching in combination with other modalities to communicate ideas about design. Intelligent design feedback requires research on how designers want to interact with their tools, and how such interaction can be managed. This paper presents a research plan for developing an intelligent multimodal design studio. We will describe recently completed, ongoing, and planned empirical studies, as well as system components that we have built and plan to build.