Role-Based Access Control models are currently considered as the most effective approach for engineering access control systems. In this paper we experiment their application in the context of Multi-Agent Systems (MAS), by discussing the design of an access control system with an agent-oriented methodology such as SODA. In particular, we show how a clear separation between mechanisms and policies can be achieved by organising the access control system along two layered sub-systems, and discuss the advantages of such an approach.