## 5 Conclusions  
In this study, we developed a construction cost estimation model that can be utilized in the early phase of a construction project based on BIM, assuming the architectural planning stage. Model validation confirmed that the accuracy of the developed model was higher than that of the conventional floor area-based model, and that the proposed model satisfied the accuracy range of Class 5 according to the AACE standard. In addition, the developed model could produce estimation results in this stage with estimation errors comparable to those corresponding to Class 1-3, the subsequent construction project stages. The significant contributions of this study can be summarized as follows. 1. Compared with the previous studies in which data from dozens of construction projects were used, this study used a dataset containing information from more than 900 construction projects to overcome the limitations of the existing studies, owing to the small amount of data. In addition, the reliability and validity of the proposed method were verified by developing a construction cost estimation model employing a parametric method that is a highly effective approach when there is insufficient information available for a given project and data. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & **(a)** & **(b)** & **(c)** & **(d)** & **(e)** \\ \hline
**Percentage Error (\%)** & +9.266 & +1.234 & –6.634 & +12.918 & +17.341 \\
**Estimate Class** & Class 2 & Class 1 & Class 2 & Class 3 & Class 3 \\ \hline  & **(f)** & **(g)** & **(h)** & **(i)** & **(j)** \\ \hline
**Percentage Error (\%)** & +0.392 & –5.908 & –4.414 & –0.409 & –29.998 \\
**Estimate Class** & Class 1 & Class 2 & Class 1 & Class 1 & Class 4 \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Evaluation of AACE conformity of parametric prediction model in planning stage. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & **Previous** & **Previous** & **Previous** & **Previous** & **This** \\  & **Study 1** & **Study 2** & **Study 3** & **Study 4** & **Study’s** \\  & **Prediction** & **Prediction** & **Prediction** & **Prediction** & **Prediction** \\  & **Model** & **Model** & **Model** & **Model** & **Model** \\ \hline Average Percentage & & & & & \\ Error (\%) & 16.20\% & 11.61\% & 8.20\% & 9.29\% & 8.85\% \\ Estimate Class & Class 3 & Class 3 & Class 2 & Class 2 & Class 2 \\ \hline \hline \end{tabular}
\end{table} 
Table 9: Performance comparison with the prediction models of previous studies (Table 2). 2. Based on the validation results of the developed cost prediction model, in the early phase of a construction project, when the design information has not been confirmed and the availability of information to be utilized for construction cost estimation is limited, the BIM setup with an LOD corresponding to the planning stage can be utilized for construction cost estimation with high accuracy. 3. In addition, the effectiveness of the proposed validation process suggests that modeling is possible by integrating the BIM design process and the construction cost estimation process. The results of conceptual cost estimation, which are the criteria for determining economic feasibility and validity in the early stage of the project, serve as the basis for decision-making, and the reliability of information provided during this stage is directly related to the success or failure of the project. Therefore, the construction cost estimation model developed in this study, capable of deriving estimates with high accuracy, can be considered highly suitable and applicable in the BIM design process. The several avenues of further research and development are as follows:
1. This study was focused on construction cost estimation, but the current utilization status in actual practice is limited to the financial feasibility analysis of construction projects, utilizing the approach of categorization into hard cost/soft cost.