In Japan's construction industry, techniques of producing complex three-dimensional (3D) formwork at construction sites are conventionally developed using the sophisticated skills of carpenters. Inspie of the development of digital technologies, the production of free-form shapes faces considerable cost and time management risks that require pragmatic solutions. In the efficient building of freeform shapes, the continuous surface should be divided into portable elements for formulating production plans and for making products in the factory. The products should then be installed and assembled at the construction site. Hence, new methods with computational design are assumed to require an approach different from the traditional processes of designing and constructing with two-dimensional (2D) drawings. This research aims to analyze the productivity of these conventional means and propose a New Method of constructing free-form formwork for real-scale buildings. First, we focused on how the designed geometric coordinate information is translated for construction on complex wooden formwork. We revealed how these shapes were realized by carpenters, and organize cases from 1991 to 2020 to see how the existing Japanese wooden formwork technology can realize double-curved surfaces. Second, we focused on a completed project that has a 5,100 m2 free-form RC roof constructed using the nonuniform rational B-spline (NURBs) curve and conventional production methods. Additionally, we analyzed the project's production time and cost from the construction records and revealed that the methods heavily depended on on-site labor. Finally, based on the analysis results, we propose a production method in which curved surfaces are divided into portable units to reduce on-site labor and ensure high accuracy. We also analyzed its productivity through some assembly experiments. The labor cost of the New Method is lower by 93% than that of the existing method.