Recently, various procurement methods have changed. And decision-making at the beginning of a business lacking information regarding bidding is being made. Thus the importance of conceptual estimate , which are the basis for decision making, is increasing. In addition, the necessity of the construction and remodeling of school facilities is increasing. However, in the existing research, there is little analysis of school facilities. In addition, research on space classification, usage and analysis of main materials is important in the initial project construction cost estimation but insufficient. So, the purpose of this study is to construct interior work packages for calculating interior finishing work by analyzing the existing BoQ document and quantity statement of the school facilities and correlating the space, site, and work information used at the cost estimation phase. Conceptual estimation research method using interior work package is as follows. First of all, through theoretical considerations, the concept and scope of the estimate and interior finishing work are summarized. Secondly, the composition of the spaces, parts and finishing materials are classified according to quantity calculation sheet of the finishing work. The space composition according to the space classification by use, reconstruction of the finishing work, and the main material of the space are constructed. This configuration constitutes a interior work package. Third, the finishing materials are constructed according to the interior work package and the estimated construction costs are calculated through Monte Carlo simulation of the finish. Conceptual cost estimates are calculated by applying the estimated construction costs. Fourth, the estimated cost is applied to the case school and compared with the actual amount. This method can verify conceptual cost estimates. The analysis results indicate that it is possible to apply it to the approximate cost estimate of the basic design stage, but it is deemed necessary to review the detailed impact factors for application to the detail design stage.