The main goal of this Master thesis is design of steel and composite structure of commercial building. The building has an irregular shape with maximum axial dimensions 39,6 x 22,4 m, and height of 8,10 m measured from ground level to the ridge. Planned location of the building is in Pula at 17 m above sea level. Static and dynamic analysis was performed with Autodesk Robot Structural Analysis according to European standards for steel structures HRN EN 1993 and composite structures HRN EN 1994. Input data are previously analyzed actions on the construction, which include self-weight of structural and nonstructural elements, imposed loads, snow load, wind load and seismic load, all according to a series of norms HRN EN 1991 and National annex in Republic of Croatia. Every designed element satisfy ultimate and serviceability limit states requirements in the most economic way. Single groups of elements, because of safety, do not exceed limit state ratio over 91%, while average limit state ratio of the whole structure is 70%. Characteristic connections are designed: A) column and RC foundation connection B) column and beam connection of the main frame Screws and welds are used for connections and their limit state ratio is 91% for connection A and 85% for connection B.