warping of joists in a two way pitched roof

huangyhg

warping of joists in a two way pitched roof?
we are designing a building with structural steel framing, open web joists and metal deck at the roof.  the architect wants to pitch steel in two directions to achieve a 1/4" per foot slope.  does anyone have a feel for how much warping can be tolerated in the joists before it becomes a problem?  
because of the geometry of the footprint, there are a couple of areas where the pitch would be as much as 3" in 12' in two directions, which seems too much to me.  i know this type of warping happens frequently and would appreciate hearing any thoughts or experiences that anyone could pass on.
thanks!
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i've done exactly what you are describing.  we had a 50 foot bay where two orthogonal sides of the square bay were level and the other two were sloping down at 1/4" / ft.  no problems...worked very well and made it easy to drain the roof.  there also were no difficulties in laying down the deck.  the slope is fairly subtle.