Basically a busduct is a streched out panelboard, so you could strech out a panel board so it has the right elevation and then circuit the connecting panels to that "streched panel". Then you would have a busduct schedule to do load calcs. I suppose if you had a horizontal run and a vertical run, you could either use a couple of "streched out" panel boards to make the runs or if no load is on them, use cable tray and use notes to clarify the specifics. In Revit, one must decide what is diagramatic and what is a real 3D object and try to convey the most useful information.
this link contains solution introduced by siemens by modifiying duct setting for thier standard busway rating and it is good solution knowing that thay provide with families for accessories and project contains modified duct setting than need loading accessories families