The research conducted on the applications of Topology Optimization (TO) in the architectural field is limited. This paper proposes an alternative process and investigates the significance of assigning the right design and non-design domain in the TO process and its effects on the optimization results. The existing approach relies on defining the design domains in areas that are usually allocated for structural elements. This research challenges the norm of where structure is allocated to evaluate the results against the criteria of minimizing material. The study investigates the idea of interpreting the design domains in a more rational perspective, using an anthropometric approach to create efficient spaces with minimum material use. The methodology involves modelling a spatial structure that evaluate scenarios with different design domains, using the SIMP method. The research is part of the Material Balance Research group projects in Politecnico di Milano, where a case study is conducted on a roof canopy in an attraction park in Orlando to investigate the results on a practical project. The study illustrates the impact of assigning the right design domain on the optimization process, not only on the performative and material distribution, but in terms of meeting design criteria and creating usable spaces. It also reexamines the idea of optimization and highlights the concept of an optimized design not necessarily being the best design.