When customizing curtain panels in a curtain wall, you can exclude segments from the grid to achieve the desired result. 
 Video: Place Curtain Grids
 Video: Place Curtain Grids 
- Click Architecture tab Build panel Build panel  (Curtain Grid). (Curtain Grid).
-  Click Modify | Place Curtain Grid tab Placement panel Placement panel All Except Picked. All Except Picked.
- Place the cursor on a curtain wall, so that a preview of the curtain appears. 
- Click to place the curtain grid. 
  The curtain grid line is displayed in red. 
   
- Click segments of the curtain grid to exclude them from panels. 
  When you click the segments, they are displayed as dashed lines. 
   
- When you finish excluding segments, click Finish Current to place a new curtain grid.