Recent contributions in the field of technology roadmapping often aim to apply various numerical models and tools to facilitate the roadmapping process and enrich its outcomes. This trend resulted in the emergence of socalled model-based technology roadmapping. We consider it as the future development of the traditional documentbased paradigm. One of the general approaches to support the model-based roadmapping is to develop a roadmap's metamodel that would define it independently from the application context and link it to the existing roadmapping literature. In this paper, we attempt to create such a metamodel by generalizing and formalizing existing documentbased roadmaps. We validate our metamodel via reproducing three very different roadmaps from the literature, not included in the set of roadmaps from which the metamodel was created.