A sectional perspective is where the building is cut (like a section) and everything beyond the cut is in perspective.
Create a camera view.
You may want to hide walls in front via Hide in View to see where you are.
Tick Section Box in properties of perspective view.
(the section box will be visible but you won't be able to select the face behind you, which is the one you need to move).
Select the section box
While the section box is selected go to a plan view (e.g. a floor plan).
Use the section box grips to move the extents of the section box to where you want the cut to be.
Go back to your perspective view.