A pipe can be cut to fit an angled flat sheet at the top end using the Mitered Pipe wizard.
Miter Angle specifies the angle of a flat cutout through the top end of the pipe.
Neutral Axis Fraction should be set to 0.5 if developing the pipe from flat plate otherwise 0.0 if cutting pipe.
Dev. Segs the number of segments around the diameter that the pipe will be broken up into.
Development Start Angle the point on the unrolled cylinder that will match up with the edge to be joined on the flat plate.
Show bends When viewing the flat plate development view the bend line of each segment.