The usage of building information models (BIMs) is well established within the architectural, construction and engineering industry to improve design, engineering and construction processes and exchange project information. BIMs proved to be beneficial by enabling off-site fabrication, reduction (even elimination) of change orders and facilitating access and exchange of digital information beyond the construction phase. This resulted in exploring the potential of utilizing BIMs for assisting facilities management (FM) tasks on a daily basis. Although there are mechanisms (e.g., COBie) to enable delivery of design information to the FM phase, the challenge is the need for customized facility information for operators when they perform FM tasks such as space management, and maintenance. Previous studies showed that BIMs should be customized for the requirements of an FM task at hand. Towards that vision to automatically customize BIMs for an FM task, the objective of the study is to identify the facilities operators' requirements on as-built BIM, with a focus on the maintenance of HVAC systems. The study builds on the level of development (LOD) and industry foundation classes (IFC) efforts to depict the level of detail of the geometric, spatial and semantic facility information during requirements elicitation phase with facility operators. The paper reports the initial findings of the requirements and LOD of the information for HVAC system maintenance.