In this paper a mass appraisal methodology for the periodic reviews of the market values of special properties that constitute the asset balance of relevant real estate portfolios has been developed. Using the information published by Italian databases, a study sample of office properties of medium and large size, located in the city of Milan (Italy) and sold in the last decade, has been obtained. After having identified the main characteristics that contribute to the formation of property prices for the study sample considered, a model for the “quick” assessment of similar properties for intended use and explanatory variables of the prices and located in the same territorial context has been defined through the implementation of a genetic algorithm. The methodology developed satisfies the need to perform repetitive valuations, that should be not only contextualized to the spatial characteristics, but also timed to the different stages of evolution of the property cycles.