Steel girder cages are widely used as plant buildings ceilings, bridge vaults, locks of hydraulic engineering constructions and other construction objects. An important task in case of their designing is the search of the most economic constructive decision with the smallest amounts of material. Therefore the great value in construction mechanics is attached to the development of methods of search of the most rational and optimal constructive solutions. The new technique of alternative engineering of steel girder cages with various cell forms, i.e. rectangular, triangular, rhombic and other, is offered. The technique is based on the principles of physicomechanical analogies and geometrical methods of construction mechanics. As a research object for a numerical example the girder cage of 12 x 6 m is considered. It has brick walls supporting. Girder profile is made of rolled sections, flooring is steel and solid. The studies showed that using a rhombic cage is the most economic.