In the architectural heritage field, a complete and in-depth knowledge of the assets is indispensable for any restoration and conservation strategy. In this context, the Historical Building Information Modelling (HBIM) technique is gaining much interest in supporting the diagnostic phase and the design and management of conservation activities. The HBIM provides opportunities to collect, organize and integrate information coming from different sources, inspections, and diagnosis techniques as well as to use standardized and effective tools for orienting cultural heritage asset management. This study addresses the challenges of developing HBIM for large-scale assets, that require adapting the conventional workflow to deliver results in a reasonable time. To this aim, a novel procedure involving a fit-for-purpose Inventory form and a scan-to-BIM approach is proposed. The data acquisition process is speeded up using multiple surveying techniques, and the modelling and information phases benefit from the interoperability among different tools that are already known by professionals in the field. As such, the main innovation lies in the ability to oversee the entire process through a single software, ensuring centralized and efficient control. This innovative process has been applied to investigate a significant portion of the city walls of Pisa, proving its ability to support the decision-making phase for planned conservation of large-scale architectural heritage. The emphasis is on the all-encompassing, interdisciplinary understanding of the assets across different scales. The suggested approach ensures a swift yet precise and reliable outcome in the diagnostic process and facilitating the critical temporal assessments and the review of information by any actor involved in the conservation.