The construction of modern buildings and structures requires careful analysis of load-bearing structures, especially monolithic slabs, which play a key role in the stability and durability of buildings, and key role in ensuring the stability and durability of buildings. Correctly specified parameters of beams and columns directly affect the deflection of slabs, which, in turn, determines the reliability of the entire structure. In the conditions of increasing number of floors and increasing loads on buildings, the relevance of research in this area becomes especially important. In this paper, the influence of beam and column cross-sections on the deflection of monolithic slabs in four-storey buildings is considered. The study was carried out using LIRA CAD software package, which allowed to obtain accurate data on the behavior of structures under different loads. The results of the work will help design engineers to optimize the parameters of load-bearing elements, providing a balance between strength and economy.