You may have to adjust its xyz location before finishing the mass which can be accomplished in plan or elevation.
Revit mass roof.
When that happens to me i remove the family remove the massed roof reload it and then try and make it.
If your design is quite simple you will not want to spend to much time on your roof.
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 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.
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5 once located properly use the roof by angle tool to generate a roof using any roof type.
This mass cannot be reused in other projects.
Family parameters and materials can be applied to mass families and elements like roofs floors etc.
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Open a view that displays the mass.
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.
Optional on the options bar specify the level of the roof.
Create a mass that is specific to the context of the current project.
Click massing site tab conceptual mass panel in place mass.
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.
Just load it into the project adjust dimensions materials etc.
Mass are quite easy to make but using this method might be require a lot of works.