Like any other data system, data lakehouses require the application of effective governance strategies and models for ensuring compliance, security and quality of the data they host. The absence of an effective data governance strategy can seriously compromise data analysis and decision-making processes in data lakehouses, reducing trust and compromising data usefulness. Despite the various initiatives carried out on the field, there are gaps in the definition and application of governance models in data lakehouse environments, particularly concerning data lakehouse system development methodologies. After studying the recent development models, architectures, and methodologies for data lakehousing, we designed a specific data governance model for data lakehouses, creating a roadmap for its application to the various stages of system development. In this paper we present and discuss such a model, as well as its concrete application to the development of a concrete data lakehouse application.