That will be because complex shapes in Inventor, as in the real world, can not be flat patterned ie Radius Elbow Bends ,"U" and "S" Bend pipes and tubes. These are usually, bent on a pipe/tube bending machine form a straight length of pipe or tube, or alternately made up of several welded up segments that are rolled from flat.
Best way is probably to draw a segment, build your shape as an assembly, show the flattened & dimensioned segment in one sheet of an IDW and the Finished shape (assembly)with dimentions in another sheet.
I don't do much sheet/plate steel wok of this type but this is usually the way I do it.
================ Thanks in advance for any help & advice
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