In the view properties expand the underlay drop down and select the level on which the roof was created to display as an underlay.
Revit create roof plan view.
This view should ideally have been generated from the level that will act as the host or base level for your new roof construction.
In the drawing area select the arc line.
Creating a roof in revit roof by footprint go to your desired plan view to begin modelling you roof.
But for whatever reason my a dash roof does not exist.
Create a plan view click view tab create panel plan views drop down and then click floor plan reflected ceiling plan structural plan floor plan reflected ceiling plan structural plan in the new plan dialog.
Your downpipe elbows should automatically generate via the revit autorouting.
On the properties palette specify a value for number of full segments.
Open the plan view of the level in which you want to see the roof line.
If you specify zero segments the default a.
This makes the roof line visible in the plan view but the lines appear as solid lines.
Navigate to a suitable elevation view west elevation in the example next go to systems tab pipe draw your desired gutter downpipe run.
Next navigate to the architecture tab roof dropdown roof by footprint as per the image below.