if we add feature layers to our scenes, e.g. to extrude 2d polygons for planing purposes, its possible to set elevation mode either to ground, relative to ground or scene or to absolute height, including fixed offsets.
Problem is, using ground/scene as base elevation the extruded Features follow the terrain, which is not nice with Buildings.
Using absolute elevation mode requires 3d-features, which is more laborious to create, not even possible directly in AGO as far as i know.
So what we miss is just an option to set base Elevation to an attribute field!
E.g. if we could choose an attribute field as an offset in the absolute elevation mode would do the trick...