The simplest method would be to give the 2D mass a nominal thickness such as o.4mm (Revit Limit) and this will then give an area and just ignore the volume.
I am pretty sure you cannot schedule or create Material Takeoff for Mass Materials.
Jay Colcombe
Autodesk Certified Instructor
Revit Architecture & Structure Certified Professional
AutoCAD Certified Professional
B.Sc. Hons Civil & Structural Engineering
If you find my post interesting, feel free to give a Kudo.
If it solves your problem, please click Accept to enhance the Forum.