Mass are quite easy to make but using this method might be require a lot of works.
Revit mass roof.
From my experience with revit it is one of those quirks that have no apparent explanation.
This mass cannot be reused in other projects.
Family parameters and materials can be applied to mass families and elements like roofs floors etc.
In the type selector select a roof type.
Enter a name for the in place mass family and click ok.
Click massing site tab model by face panel roof by face.
Please like this tutorial.
For your information a parametric gable mass is already available in the revit libraries in the mass folder.
When that happens to me i remove the family remove the massed roof reload it and then try and make it.
Create a mass that is specific to the context of the current project.
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Amazing that a user in a revit related forum is advised to go to another application archicad 16 to do a simple gable mass to represent a sample house in a site.
If your design is quite simple you will not want to spend to much time on your roof.
If that does not work i hack it and use a wall in place of a roof and see if that works.
First you can create a mass and create roof by selecting the mass faces.
Click massing site tab conceptual mass panel in place mass.
Optional on the options bar specify the level of the roof.
Revit model space lets you work simultaneously with in place masses system families and mass families conceptual mass families.
Just load it into the project adjust dimensions materials etc.
Get these project files and all advanced courses.
I will not discuss much about this for now.
Generate revit roof in revit create a new mass and import the sat file from the previous step.