Answer:
When using user-defined cross-sections in Revit, you can create them in RSECTION and control them for the export to RFEM 6.
Creating Cross-Section Template Using RSECTION
Import your RSECTION cross-section into RFEM 6:
FAQ – Import of RSECTION Cross-Section
Then, save the RFEM file as a template (*.ft6 file):
FAQ – How can I create a model template in RFEM 6?
Referring to Template for Revit Export
When opening the Export dialog box in Revit, you have the option to define the file path for an RFEM model template (*ft6 file). Select your previously saved template file for this.
Then, you need to save the conversion in the conversion tables in Revit for the RSECTION cross-section.