The green building philosophy has recently taken a central role in the construction industry, mitigating the environmental impact of buildings. Buildings are responsible of a large portion of harmful emissions and use a large fraction of the total natural resources. Moreover, the bad quality of indoor environments in office buildings can affect the health of employees, reducing their productivity. Because materials used in construction projects are responsible for a significant fraction of this environmental footprint, a better selection and use of materials could lead to a green certification such as the one given by the Leadership in Energy and Environmental Design (LEED) rating system. This paper illustrates how an optimization model can be used to help decision makers to select the right materials, incorporating design and budget constraints while maximizing the number of material-related LEED-based credits. A case study based on real data is analyzed from different angles to demonstrate the effect on the optimal choice of materials due to changes in construction market conditions. Copyright ASCE 2009.