I will present work done by my group on defining a collaborative construction task that allows us to use the Minecraft platform to study situated natural language generation and understanding. In this task, one player (the Architect) needs to instruct another (the Builder) via a chat interface to construct a given target structure that only the Architect is shown. I will discuss what makes this task interesting and challenging. I will also describe models that we have developed for the Architect and the Builder role, and discuss what remains to be done to create agents that can solve this task.