A decision making system is proposed to run building projects in Malaysia and is known as System Dynamic Model. The project is under Public Private Partnership University's student accommodation. The issue exists when the private sector failed to make decision making in determining certain financial variables such as Building Lease Charges since it affects the project IRR. This IRR is an important mark for a successful project. However, it is determined by the public sector, which delays the decision making process. Furthermore, contradiction in determining this variable could arises between the sectors. In the process of making decision to determine the variable, there will be recurring revision of previous system (financial model) including recalculation and restructuring the building lease charges amount. Hence, it makes the process too complicated and slow. Therefore, this paper aims to develop System Dynamic Model (SDM) as an alternative approach to make decision faster when determining Building Lease Charges and facilitate the process of making decision. Moreover, this SDM can simulates and analyzes the sensitivity of building lease charges to the IRR. The methodology is based on quantitative technique. Data is collected and a case study on a PPP university's student accommodation project is used. From the research results, the parameters of Building Lease Charges which affected to the Project IRR within range 16% is RM38-RM39. The sensitivity histogram generated that there are 21 simulations for which, at time 23, Project IRR is between 17.6% and 21% and about 2 simulations in which it is between -2.8% and 0.60% The results give substantially more information than an expected Project IRR in making that judgment. It is proven that SDM could solve the problem for the associated determination of building lease charges. It is expected that the SDM can generate knowledge among researchers in solving the complex situation managements especially in real big development, investment and business projects.