Cost estimating is essential in decision-making for conducting project management on early design stage. The cost estimating method for each stage varies according to level of design detail. Therefore, in the cost estimating method for each stage, it must distinguish quantity items that can be directly measured from quantity items that should be predicted. The parametric estimating method is able to support cost planning for various design attributes as it is possible to set impact factors related to design features as parameters. This study suggests a prediction method for quantity information that is required to estimate the final cost during the early design stage. The case study suggests an predicting method for the steel (rebar) ratio of office buildings. The suggested parametric cost estimating model enables users to predict the steel (rebar) quantity for various design alternatives according to design features. During quantity predictions, IG(Information gain) measurements for the design attributes were analyzed, by setting the ratio of steel-rebar quantity(Ratio: ton/Concrete_㎥) as the dependent variable.