substantially parallel to the sloping floor 12 of the building each chair 30 includes a web 34 extending upwardly from a base plate 32 the chair 30 supports the end of the upper member 18 of truss 16 and is mounted on a bearing plate 36 on top of column 14 and secured by bolts 38 in this manner the truss 16 is supported at each end near the top of the respective columns 14 with the end upright members 22 of each truss 16 being adjacent but unattached to the respective columns 14 in such a manner that the truss 16 when oriented parallel to the floor 12 of the hangar h is at either a slight acute or obtuse angle depending on the slope to the respective columns 14 a fairly wide face plate 26 is affixed to the top of the truss 16 immediately under the upper member 18 e g by welding to provide a surface on which the upper edge or beam 42 of the door 10 can be attached in a horizontal line in spite of the overall sloped orientation of the truss 16 the upper edge or beam 42 of the door 10 is shown in fig2 in phantom lines attached in a horizontal orientation to the.