For your information a parametric gable mass is already available in the revit libraries in the mass folder.
Revit mass roof.
Enter a name for the in place mass family and click ok.
In the type selector select a roof type.
5 once located properly use the roof by angle tool to generate a roof using any roof type.
Revit model space lets you work simultaneously with in place masses system families and mass families conceptual mass families.
I will not discuss much about this for now.
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Open a view that displays the mass.
Optional on the options bar specify the level of the roof.
First you can create a mass and create roof by selecting the mass faces.
Create a mass that is specific to the context of the current project.
Just load it into the project adjust dimensions materials etc.
Please like this tutorial.
Click massing site tab model by face panel roof by face.
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.
Click massing site tab conceptual mass panel in place mass.
Generate revit roof in revit create a new mass and import the sat file from the previous step.
Mass are quite easy to make but using this method might be require a lot of works.
If your design is quite simple you will not want to spend to much time on your roof.
Family parameters and materials can be applied to mass families and elements like roofs floors etc.
If that does not work i hack it and use a wall in place of a roof and see if that works.
Get these project files and all advanced courses.
From my experience with revit it is one of those quirks that have no apparent explanation.