The paper presents the process of designing and dimensioning a full flat girder, and then selected the profile of the girder that met all the necessary conditions and criteria of the business facility Atlantska plovidba located in the city of Dubrovnik. Solid flat girders and their application in structures are described, and the calculation of internal forces is presented on the example of a simple structure. A selection of load-bearing structure, substructure and roof cladding materials was also made. The paper presents the calculation of constant loads due to its own mass and variable load due to the action of wind on the structure. Characteristic and budgetary values are taken into account. A comparative mass of all profiles of solid flat girders was performed and shown because the minimum mass is an important selection criterion. Using the analytical hierarchical process (AHP), the significance of individual criteria and the weight of the criteria were determined, and the concepts of cover selection were evaluated. In the end, the justification was shown by the degree of goodness and the best material for the roof covering was chosen.