Hi I do this kind of thing all the time as I work mostly in interiors, if you assign your materials to the piece of furniture then export it in the .3DS format then using the Archicad 3DS import command to bring in the file, I then turn it into a morph turn on the fills & pens etc that I require and save the object as a GDL object into my library, I have built up a huge Archicad library of furniture lighting and accessories it's at 16.3 GB now & growing.
I have attached a screen grab of the Archicad command that I use, I hope it helps.
Regards
David
