This paper presents a conceptual model of negotiation support for building system selection. Building system decomposes a building project into a collection of systems and system components. The model has been test to the decision in an office-building project. Model of decision has been set based on ASTM international standard of building economics. The standards are (1) E1699-00: Value Analysis of building and building systems, (2) E1765-02: Analytical Hierarchy Process to multi attributes decision and (3) E2013-99: Function analysis during value analysis study.