Office buildings are the real estate market main component which based on a low rate office space offer and an increasing request during the 2005-2008 years attracted the biggest part of the investments of that period. The real estate investor main goal is to obtain the highest possible profit rate. One way to obtain this is by reducing the initial costs for an investment. Taking into account Bucharest’s high seismicity level, based on our experience the office building structure can represent up to 30% and even more than this value, from the total building cost, which makes a studied structural solution, from technical and economical point of view, an important profitability component. According to our studies made for more Bucharest high buildings it results that the optimum structural solution for high office buildings is the reinforced concrete and steel as construction materials combination, with their advantages. Combining the two materials we obtain a structural system with two main components: the horizontal forces resistance component represented by the reinforced concrete shear walls and the composite gravitational structure represented by the composite light floors supported by composite columns. An example of an office buildings recently built in Bucharest using this system are the two towers part of the “CITY GATE” office building complex.