The behavior of a human being in a building, its activities, its interactions with it and with other people are certainly a highly complex phenomenon extremely hard to predict and evaluate. At the same time, the response of a built environment to future users needs is one of the key factors of its performance. The Agent-based Modeling paradigm is considered potentially the best way to represent human behavior but, in the building design field, its experiences are limited to representation of partial aspects of human behavior in discrete events. Currently, a more "extended" representation of human behavior able to offer an overview of the human activities related to the building “functioning” is missing,. This lack is due to the complexity of interaction among users and built environment, and to the extensive knowledge, provided by different disciplines, needed to reliably represent it. The proposed research focuses on the construction of a general representation template of user-actor, easy to implement and flexible enough to structure the large amount of data affecting human behavior. The development of the ontology-based template shown in this paper can lead to a user-agent's entity whose parameters and behavioral rules can encode and represent several “aspects” of real users and their interactions with the other entities (building components, furniture, other people) in a built environment.