We describe a collaborative research effort between the faculties of Computer Science and Architecture, investigating a special-purpose visual language to be used to generate architectural forms. This language forms part of a larger system intended to automate the process of generating architecturally designed houses. The rules which can be specified using the language described here are used to prune a set of floor plans according to specifications provided by an architect. They are intended to replace rules written in Prolog, allowing the architect to directly specify and understand the rules.