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