Many building companies have continuous attention to sustainable design of steel structures utilizing advantages of stressed skin action. The implementation of such approach for the open plan buildings might give considerable savings of material and erection time. However, in many cases, the structure of roof trapezoidal sheeting that transfers load on the long sides of the frame to wind bracing is described by simplified analytical model and different effects of diaphragm behavior are neglected. Thereby, for instance, FOS may be overestimated, but the benefits of stressed diaphragm effect, in comparison with common framework, would be unnoticeable. On the other hand, complex FE-models are able to describe structural behavior of the roof diaphragms frame to some extent but such models usually require huge computational resources. Therefore, in this work, the alternative approach for designing of lightweight frames of the roof is demonstrated for the hangar building. Firstly, 3D-models of the hangar and its roof are considered and solved accurately using mixed shell-beam-solid FE. The combinations of loads on the structure are considered in accordance to relevant Eurocodes, with special emphasis on the lateral loads. The problems of structure stability and stiffness are solved in detail. The cross-section shape of sheeting for the roofs, as a crucial factor of buildings stiffness, is parameterized using CAD based NURBS curves in such a manner that number of control variables is minimal. Next, for the purpose of reduction of computational time, metamodels are created by recently developed original code “KEDRO” for design of experiments, analysis and multiobjective robust optimization, so cross-section shape of sheeting is bound to the structure responses. Finally, cross-section shape of sheets subjected to different load combination is obtained by global stochastic search procedure to maximize stiffness of stressed elements and at the same time with constrained mass, appropriate stresses and deflections.