## 6 Conclusions  
Free-form buildings are known to be difficult to construct due to their unique facade shapes and nonconformity to conventional building techniques. Free-form facades require cutting-edge accuracy in the design, penalization, optimization, fabrication and installation of facade panels in order to be delivered as intended by designers. Therefore, utmost care should be taken during each of those stages as any mistake could lead to dire consequences for the project. The choice of material and method of production of the facades has always been a point of concern for the free-form designer and contractor. The panels of free-form facades involve three categories in terms of their curvatures, i.e., a planar, a single-curved, and a double-curved panel. Quality of the panels is determined by the geometric difference between as-built and as-designed panel shapes. The difference causes the discontinuity of the facade curvature lines and distorts the overall beauty of the buildings. According to previous research, among the three types of the panels, the double-curved one is very difficult to form and shows bigger quality discrepancy than the other two panel types. The main objective of this study is to identify empirical lessons learned for the small/mid-scale contractors on which they can enhance capacity of managing the as-built quality of the curved free-form panels. To meet the research objective, the study performed a case study of a small free-form building and the mock-up tests of curved panels. Among diverse materials, the study focused on the aluminum and GFRC panels. The two materials have been the most widely used as free-form panels. The case study subject study was a small free-form building called Haewoojae and showed how to measure the as-built quality of the free-form panels and how different the as-built qualities of the three panel types would be. The as-built BIM drawings of Haewoojae were obtained by 3D laser scanning technology and compared with the as-designed drawings by the superimposition technique. The results of the comparison showed that the installed facade panel data deviated from the originally planned design data as the previous research had pointed. In order to make the findings more reliable, eight mock-up panels made of aluminum and GFRC were designed and fabricated by conventional panel forming methods including bending, hammering, and molding. The panels of each material were of three curvatures types including planar, single-curved and double-curved panels. The data of the double-curved panels for both aluminum and GFRC were found to have certain deviations which exceeded the Korean standard allowance limits. This would pose problems like twisting at the time of fixing a number of panels side by side on the mainframes and sub-frames of the free-form structure. This twisting could also lead to other defects in the long run, among others including bulging, leakages, and falling off of some components. The mock-up panels were made by two companies, which had fabricated metal sheet panels and GFRC or FRP panels in Korean construction market. Six managers and engineers involved in the mock-up panel production were interviewed to figure out their opinions and perception regarding necessary approaches to securing the as-built quality and to come up with certain lessons for handling the difficulties in forming free-form facade. The interviewees highlighted the necessary understanding of the distinctive features of materials to use. They figured out the biggest drawback of metallic materials was springback and three factors, i.e., size of segment, bend angle, and bend curvature, critically influenced the amount of spring-back of metal. They pointed then that the cost of forming free-form panels obviously differs depending on the shapes of the panels and the forming techniques to produce the panels. The author investigated the unit costs of fabricating the mock-up panels on the four panel types.