This thesis is the project of replacing the steel roof construction and the outside fire staircase with elevator of the UL FGG building on Hajdrihova street. First we determine the loads for the roof and the fire staircase. Then we make a 3D model in the program Steel Engineer in order to calculate the internal forces. For the main structure of the roof we select the frame in one direction and frame with centric bracing in other direction. The fire staircase has four internal columns and four external columns around which vertical bracing is placed. Between internal and external columns there are stairs with intermediate platforms. In this project we make the ultimate limit state analysis and seismic analysis for both designs. The seismic analysis is performed using a simplified method of horizontal forces. At roof seismic analysis is used to design vertical bracings and to design the rest of the elements we use the ultimate limit state analysis. At fire staircase seismic analysis is used to design columns, beam and vertical bracings and the ultimate limit state analysis is used for the rest of the elements. In both cases we also design joints and draw the position and detail plans.