It is easier from SketchUp.
Model whatever, save it as a component in Sketchup, open the Sketchup file in Archicad using the plugin. It will be converted to the library part, with materials.
Advice: this has been discussed umpteen times, and I have typed the above sentence at least four times. Do a
Search before you ask a question many people before you have asked.
Djordje
ArchiCAD since 4.55 ... 1995
HP Omen