Urban areas and relative built heritage may be exposed to different types of risk, according to their specific features. Safety management of civil infrastructures should be oriented towards a multidisciplinary approach to achieve a holistic analysis of risks (both natural and human made). In this perspective, the GRISIS research project (Risks and Safety Management of Infrastructures at Regional Scale) aims at developing a multi-risk technological platform for Campania region, in South Italy. It allows to gather and store different types of data concerning the area of interest, thus providing essential information in order to conceive methods and tools for management and mitigation of multiple risks to infrastructures and building networks. This paper focuses on the proposal of methods and tools for the management and mitigation of seismic risk on infrastructures and building networks, developed within GRISIS project framework. Tolerable seismic risk levels for an existing building are a balance between the reduction of risk and the cost of rehabilitation. This study attempts to develop a decision-making procedure to figure out how to distribute the available budget in order to get the maximum possible portfolio risk reduction, identifying how to intervene on each single building. The proposed seismic risk mitigation strategy is uploaded in the GRISIS multi-risk technological platform, creating an interactive user-friendly tool, available online, that provides the best economic resources allocation after selecting the available budget for a specific portfolio of buildings.