Hubert Wagner:
Yes, for top, bottom and side material (end material implies a rectangular shape, this command, like Prism_ command, is for any polygonal shape) in the GDL Reference Guide see:
CPRISM_ command. There is also a
BEAM command that gives the material options similar to a Beam.
You should add a Signature to your Profile (click the Profile button near the top of this page) with your ArchiCAD version and operating system (see mine for an example) for more accurate help in this forum.
David