I'm not sure how ArchiCAD 18 does it but in ArchiCAD 19 in the Scheme Settings using the "
Add..." pop up/button click the black triangle and it gives you the option to add parameters from either your objects or your IFC settings
AC versions 3.41 to 25 (UKI Full 5005).
Using AC25 5005 UKI FULL
Mac OSX 10.15.7 (19G2021) Mac Pro-2013 32gbRam AMD FirePro D500 3072 MB graphics