Creating a Surface from 3D Polyline

Background Information: I am trying to determine by how much the exposed surface area of clay in a small metal cup (top inner diameter: ~45 mm, bottom inner diameter: ~40 mm) changes as it dries and shrinks. I have made two models using photogrammetry; (1) clay is wet, and (2) clay is dry. I created a model of the cup interior using SketchUp, and extracted the surface area of the wet clay by finding the line of intersection with the cup model. The dry surface area is giving me problems, as the clay has pulled away from the cup walls, thereby exposing the side surface of clay, but isn’t captured by the photogrammetry. My proposed solution is to draw a polyline along the perimeter of the top surface, and then create a side surface by extruding it downwards until intersecting the cup. It’s not a perfect solution, as the clay might not be pulling away totally evenly, but it should be good enough.

Problem: I can’t seem to find a way to extrude the perimeter 3D polyline downwards to create a surface that can intersect with the interior cup model. Does anyone have any advice on how to do this, or perhaps alternative solutions? I have access to Agisoft Metashape, CloudCompare, Civil 3D, and SketchUp Pro to create alternative file formats or workarounds. Thank you!

Tig’s Extrude tools has an extrude edge by vector which would do that.

Thanks @Box that worked!