Display a floor plan view or a reflected ceiling plan view.
Revit roof plam.
In the view properties expand the underlay drop down and select the level on which the roof was created to display as an underlay.
Normally when you are modelling a roof in revit you will have a level set up to control it s height this may by a level that is also controlling the top of your external walls.
Tutorial on roof construction modeling in revit.
Make sure the floor plan view you choose to work in is associated with the level at which you want to create your roof at.
Click architecture tabbuild panelroof drop down roof by footprint.
Some may call this wysiwyg or what you see is what you get.
If you try to add a roof on the lowest level a dialog prompts you to move it to a higher level.
Out of the box revit doesn t do this because revit shows it as it s built.
If you choose not to move the roof to a different level revit notifies you later if the roof is too low.