The material presented in the article is devoted to solving the actual problem - the improvement of traditional design solutions of spatial roof structures with overlapping of long spans with atypical ratio of the lengths of the plan sides. In this regard, the main objective of the research is to establish functional relationships between the geometric parameters of the projected spatial roof structure and its size in terms that will use a standard set of structural elements. As the object of research, in this case, is considered the structural roof of the MArchI system at unconventional plan 68,4h45 m. The proposed approach provides solutions for the control of the parameters of the stress-strain state and are based on two principles: the changing of local geometrical parameters (size of roof cell – it’s height), and reverse arching of initially flat plate, that is, changing of the overall geometric shape. Fine depending allows the use of standard modular elements of the MArchI (rods and insert-connectors) at designing roofs on non-standard plans. For a more complete assessment of the effectiveness of the proposed approaches for the first time estimated the impact of support structures compliance on the parameters of the stress-strain state (the maximum force in the rod element and the maximum deflection). In order to generalize the results of the research required parameters are shown in relative form as a functional dependence of the parameter k, which characterizes the compliance of the support structures. These studies established that: - the required value of the initial reverse arching for a shallow shell is f / l≈1 / 27, that is a motionlessly fastened on a contour, and for which it is possible to use standard components of MArchI type- the use of a reverse bending is an effective method of controlling of the SSS parameters for the case of "rigid support" of structure. When the designing roof is located on elastically compliant supports this method is most effective when the ratio h / l = 1/50, - a developed depending «k - w / L» and «k - N / [N]» are nonlinear and allow to establish a significant impact of compliance of support structures for roofs with low relative height (1/40) L ... (1/50) L. The findings in addition to the scientific value have practical significance to facilitate the initial stage of the design process in the appointment of the geometric parameters of buildings in compliance with the above restrictions.