In this article it was analyzed how does structural system for long-span roofs behave under the loads in order to determine the rationality of using such constructive scheme and its geometric parameters on example of Polytechnicheskaya metro station in Saint-Petersburg. In the course of the work, the finite-element model of the coating was calculated. Then its height was varied using seven different types of computer models. Calculations were done in SCAD 21 software complex. A technical and economic comparison of different covering options was carried out to determine the height of the structure, which leads to significant decrease of internal forces to reduce the costs. It was proved that the applied approach is efficient and economical.