If it is level side to side (and a constant width) then you could use the railing tool.
Create a custom profile rail the shape of that envelope.
Then place the rail along one side of your site.
If you crate a contour line on the mesh, you can even just magic wand it to that line.
Or there has been work done on a polyline profile object.
Maybe this can help (not sure), but again I think the profile has to be a constant size/shape as it follows the path.
https://archicad-talk.graphisoft.com/viewtopic.php?f=49&t=69913
Barry.
One of the forum moderators.
Versions 6.5 to 27
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