Dwayne,
Juha and Aussie John have already given you the answer but here is an example I did in AC 12. I held back the plane from the corners slightly, rather than extending it beyond, to improve the 3D appearance but not so much that a gap would be visible with a reasonable line weight.
By the way you should on the Profile link above and fill in the Signature block with your ArchiCAD version and system OS. Answers to some questions can depend on this information.
Erich
AC 19 6006 & AC 20
Mac OS 10.11.5
15" Retina MacBook Pro 2.6
27" iMac Retina 5K