a building skeleton comprising profiled bars of rectangular profile and / or of i - profile . the rectangular bars have undercut grooves of the same size and cross section that extend longitudinally along each of the sides of the rectangular bars . the i - bars have such grooves on the outward sides of the transverse parts of the i - bars . intermediate elements are receivable in the grooves for connecting two bars having grooves laid one over the other or two bars arranged one after the other along a path . in one embodiment , smaller cross section rectangular bars are telescopically insertable into hollow , larger cross section rectangular bars . the height of a side of the rectangular bar may be the same as the height of an i - shaped bar between its transverse parts or their respective heights may be different , which enables nesting of a smaller size rectangular bar or a smaller sized i - bar between the transverse parts of a larger size i - bar .