Use the Reveal tool to add a decorative horizontal or vertical cutout to a wall in an elevation or 3D view.
 Build panel
Build panel Wall drop-down
Wall drop-down
 (Wall: Reveal).
 (Wall: Reveal). 
 Placement panel, and select the orientation of the wall reveal: Horizontal or Vertical.
Placement panel, and select the orientation of the wall reveal: Horizontal or Vertical. 
Revit preselects the reveal location on each adjacent wall.
