Ontology building is a social process requiring, as a first step, the collaborative work of a group of people to create a shared understanding of a specific domain of interest. This process typically involves an heterogeneous group of people: from ontology engineers to domain experts, to end users. A crucial aspect of ontology building is to reach consensus among all the involved actors. For this reason, it is important that every step of the process is clearly defined and the roles played by the members of a community of interest (COI) are precisely assigned. In this paper we present the guidelines for social validation in the ontology evolution process. In particular, we describe the process and we identify the milestones where the COI is asked to reach a consensus. Then, we present the different roles to be played in the COI, the procedures to reach consensus and the result of a first experimentation in the domain of semantic technologies.