Densely built-up urban areas, such as historic centers or adjacent and peripheral areas, often exhibit a deficiency of public green spaces and poor environmental qualities. Urgent regenerations of these areas are imperative to enhance the overall quality of life for inhabitants. Considering these aspects, this paper documents ongoing research aiming to propose integrated interventions on extensive public buildings or complexes including health facilities, schools, administrative buildings, and public social housing, often occupying entire blocks or extensive portions of urban fabric. Courtyards, cloisters, and nearby open spaces, coupled with substantial roof areas, provide opportunities for large-scale actions to augment permeable surfaces, expand public green spaces, and thereby facilitate adaptation and mitigation to climate change. The research aims to establish a multi-criteria methodology suitable for selecting suitable buildings and open spaces to undergo greening interventions. Following mapping, filing and classification phases, the evaluation of public buildings in this analysis considers typological, constructive, urban, and environmental characteristics to identify their readiness to undergo greening interventions and to define the most effective strategies to increase permeable surfaces, enhance microclimate, optimize botanical and hydraulic behavior, and ensure economic and durable solutions. Furthermore, such interventions, integrated into comprehensive urban regeneration strategies, transform indoor open spaces into public green areas, creating a “network of public greenways” in neighborhoods lacking such spaces. This approach contributes to human and urban health perspectives. Finally, the results of this study aim to provide robust support for decision-makers in defining effective greening interventions, both at building and urban scales.