This paper reports on the development and potential implementation of a new green office building rating index. It is intended to provide a market-driven green scoring for US office buildings that includes buildings below the level of LEED. The index data are drawn from demand-side data from tenant surveys for individual green office buildings features and from supply-side data from hedonic analysis of rent rolls. The index also includes qualitative input from institutional industry leaders on how it could be useful to them in practice in market their somewhat green office space to potential tenants. This paper details the development and first steps towards implementation of the scoring system. A variety of proposed models, including some that separate out LEED and non-LEED buildings, are analyzed, discussed, and optimized, and tested on a captive sample of 198 US office buildings. A reasonable model shows that about one-third of the non-LEED buildings score higher on this scoring system than lower-scoring LEED buildings. This indicates a market may be present for this type of index.