If you try to add a roof on the lowest level a dialog prompts you to.
Roof in revit 2020.
Select an interior wall and then right click.
Architecture tab build panel roof drop down roof by footprint or roof by extrusion topics in this section.
On the contextual tab of the ribbon select attach and then select the flat roof.
Open the 02 lower parapet floor plan.
Use a slope arrow to define the slope.
Create a roof from a building footprint or an extrusion.
On the options bar for overhang enter 600 and select defines slope.
From the contextual menu choose select all instances visible in view to select all of the interior walls.
Sloped edges on a roof sketch line create a sloped roof.
Click architecture tab build panel roof drop down roof by footprint.
This video demonstrates the following.
When using a newer software release you may notice.
Use sloped edges or a slope arrow on a roof to create sloped roof elements.
Click architecture tab roof drop down roof by footprint.
Now the interior walls stop at the underside of the roof and no longer extend through the flat roof.
Change the slope angle of the roof.
To edit roof.
Create a sloped roof with an overhang.
About roofs revit offers several methods of creating roofs.
Create a roof by footprint.
On the draw panel select a sketch or pick tool.
On the draw panel click pick walls.
Display a floor plan view or a reflected ceiling plan view.