So basically edit sketch of the highlighted roof and trace the edge of the front roof then make sure none of the new lines are slope defining.
Revit how to slope a roof.
Create a roof slope using slope arrows create a footprint roof sketch similar to the following.
Click finish edit mode.
3 modify each.
Want to create a sloped roof.
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Use a slope arrow to define the slope.
Define a sloped edge to a sketch line.
2 modify properties to adjust roof slope.
Create another footprint roof sketch at a higher level.
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Click on a roof and change the angle in the slope properties.
For example if you are sketching the roof on level 2.
8 tips to create sloped roofs in revit 1 check define slope to create a sloped roof.
In the option bar make sure define slope.
On the properties palette specify a cutoff level for the roof.
Then use join geometry to clean it up.