The Roadmap to Zero Emission suggests steps to contribute to attaining Net Zero Carbon in Indonesia by 2060 in the short, medium, and long term. One of the roadmap's components is applying the green retrofitting concept to highrise office buildings, which is crucial in reducing Greenhouse Gas Emissions. Buildings built before the 2000s are still vulnerable to the importance of energy efficiency, so renovating existing buildings through green retrofitting is necessary. This is because retrofitting allows existing buildings to be utilized for sustainability, reducing excessive energy expenditure. Green retrofitting is an effort to adjust the performance of buildings that have already been constructed to obtain a green building certification. Several governmental and non-governmental organizations provide certificates with different benchmarks and parameters for customization. Two regulations and benchmarks are used in Indonesia to assess Green Building performance: the Green Building Council Indonesia (GBCI) and PUPR Ministerial Regulation Number 21 of 2021. The implementation of customization can be achieved through the development of a Work Breakdown Structure (WBS). According to the 6th edition of PMBOK, WBS and Resources Breakdown Structure (RBS) can be used to detail the resources needed for project planning, monitoring, and control. Research results show that cost estimation accuracy is expected to improve by developing a WBS based on the Retrofitting concept guided by GBCI and PUPR Ministerial Regulation Number 21 of 2021. Furthermore, developing the BIM-5G model will enhance cost estimation accuracy. © 2025 Author(s).