Green Roofs and Green Walls, known as Nature-Based Solutions in Building application (NBS-B), are gaining attraction as strategies to help meet the 2050 decarbonization targets. This study looks at their effectiveness, both as single strategies and combined with Insulation (INS), in reducing operational energy use, increasing property value, and life cycle cost over a 50-year evaluation period, for both retrofits and new builds. Parametric energy simulations were carried out across five different European climates to evaluate building envelope performance under varying conditions. Then the city of Bolzano, Italy, was selected as the case study for life cycle cost analysis. The results show that in buildings with low energy performance, GWs can cut heating demand to 42.6% and cooling by 46%. GRs are less effective, reducing heating by 16% and cooling by 30%. In buildings with high energy performance, energy saving is minimal as the building envelopes are already optimized. Life cycle analysis shows a baseline cost of 996 €/m2 of Heated (GFA) without NBS-B, then adding GWs raises the cost to 1,467 €/m2 Heated (GFA) for retrofits and 1,634 €/m2 Heated (GFA) for new construction. On the other hand, GRs lower costs, from 661 €/m2 Heated (GFA) to 256 €/m2 Heated (GFA) for retrofits, and to 291 €/m2 Heated (GFA) for new builds. GWs save more energy, but their high costs often outweigh the benefits. GRs save less but are more cost-effective, making them the better financial choice in climates like Bolzano.