Flexural mechanical properties of regular polygon sections were studied to optimize the design of cantilever structures. The results demonstrated that square sections possess optimal stiffness and anti-deforming capabilities. The flexural stress of sections is relevant to load direction. Bending resistance capability is optimal when circular sections are used for random load, whereas squares are optimal for directional load. Engineering examples indicate that the flexural stress of sections is also associated with the ratio of the upper and lower bending moment. The column section of most billboards should be square if the upper area is larger. Otherwise, similar to road lighting, the column section can be a circle or have 16 regular sides. This is a crucial guideline for the design of actual projects.