In article problems of formation of cost of building are considered. The author offers to use budget designing as a basis of costs management in the building firm. The external and internal factors forming cost of building are considered. One of internal factors is perfection of systems of a quality management in the building firm and costs management within the limits of this system. Definition of planned and actual costs deviations of on the basis of the factorial analysis and allocation of operated deviations in system of quality management of the building firm is resulted.