the polyhypar is formed of a continuous albeit seamed expanse of web material and does not require any rigid structure except at its periphery the configuration and curved nature of the polyhypar and of curved sections 18 may be appreciated from the illustrations of fig3 b and 3c it is noted from a consideration of fig3 a 3c that each of identical sections 18 is formed of a plurality of strips of web material fig4 a shows a section 18 in perspective view indicating its curvature fig4 b illustrates the four components of each section 18 and indicates how they are cut from strips 20 of web material it is noted that while triangular outer components 22 and 24 extend to the full width of the strip the interior components 26 and 28 are tapered along both their side seams indicated by reference numerals 30 and 32 respectively on each of components 26 and 28 this tapering provides the desired curvature to sections 18 when components 22 and 24 are joined together along the indicated seams each of sections 18 is a hyparic surface sections 18 and indeed all of web material 14 may be formed of any suitable web material such as canvas plastic or a composite material reference is now made to fig5 which illustrates a building structure 40 comprising a plurality of parallel webs 42 which are mounted and arranged between generally parallel arc type ribs 44 it is a particular feature of the embodiment of the invention illustrated in fig5 that the webs 42 may be formed of different strengths of web material in order to realize net economy in web material thus.