Modern-day construction industry has to deal with unprecedented obstacles: the need for a radical digitalization and the inclusion of sustainability in an extremely polluting sector. These goals can be pursued simultaneously in a BIM environment when considering an already existent building or urban area through a "reverse engineering” procedure and the creation of a Digital Twin. This thesis aims to realize a Digital Twin of the town of Rosazza (Biella, Italy) to assess the risk of floods for existent buildings. Data about the city and flood events in the area were analyzed and implemented in a BIM authoring platform to create an integrated environment that could offer a digital representation of the city through a Scan-to-BIM approach and an efficient data enrichment phase that exploited live-data coming from a combination of traditional weather station and an innovative monitoring system through sensors.