Hi - see the attached file. I created two Icoshedra from the Polyhedron plug-in - one with scale 100 and one with scale 104. You would make the difference between those two to be your material thickness (so in this case 4 mm).
Then extract unique faces of both. In the case of the Icoshedron, there is only 1 unique face per size. Isolate the faces and create surfaces between them - I used EdgeSrf but there are many ways of doing that. In the attached file, I then put the new solid face flat on the XY plane.
Icoshedron.3dm (202.3 KB)
-wim