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