opening in structural steel roof

huangyhg

opening in structural steel roof
you can certainly engineer a truncated pyramid roof without diagonals across the upper opening or the base.  by statics, the force induced by the corner diagonal member is resisted by two perpendicular members at the compression ring or the base.  roof sheathing of some sort should be used to carry wind loads to the base and to prevent racking of the entire truncated pyramid roof.
i agree with dave...you can create a square "compression" block in the center, with the hip ridges of the roof coming off the corners of the square.  the stiffness of the square can be such that all forces are resisted.  not a big issue.