Window Treatments can make window look larger and room appear taller

If you have windows that are different heights, or you just want to make them look taller and wider, read on. The secret to getting that window to look taller and wider is to make your window treatments larger than the window that you are installing them on.  When you measure for the rod, go up above the opening at least 6" and up to 12" for that tall look. For the width, you should add 10" of space on each side for each width of drapery fabric. A width is typically 48" wide finished. If your panel has pleats, it will be about 20" wide when pleated.
If your window opening is 48" wide and you have non-functioning decorative drapery panels that will not open and close, you will want to use 4 widths of drapery fabric (2 on each panel) to make it look full and to scale. This will mean you need to have at least 20" extra on each side of the window to bring your total width of the curtain rod up to 68".
The opening of glass will be completely exposed and you will have a window that looks much wider than 48".
The images below is an examples of how to make the window look much wider.
  Also, the two windows in the room had different heights and the line of sight needed to be balanced by setting the drapery rod at the height of the smaller window. We didn't use drapery panels on both windows as the balance would have been off. Too much fabric makes the room look smaller and overwhelms the room. The use of the roman shade on the second window brought balance and helped to bring scale to the second window by making it the prominent focal point in the room.

Window is 48" wide with 60" drapery rod which allows the entire 48" glass area to show

The window is 48" and the window drapery rod is 68" wide and when it was completed, the window looked wider and more prominent in the room adding a focal point for the eye to travel to.
This helps with bringing balance to a wall where the window may not be centered on the wall.
Adding height to a window treatment can make the room look taller.
The image below is an example of how to hang a drapery rod in a room where the windows are 96" to the top of the frame, but the drapery rod is placed at 108" to bring the eye upward.

Adding 10 to 12 inches to the height of the drapery brings the eye upward

The room can appear much larger when the window treatments are installed in such a way to add size to a window width and height.  In the image below the drapery panels were hung at 108" to make the window appear to be taller. And the window is 72" wide and the drapery rod is 108" giving you 18 extra inches on each side of the window so that when the drapery panels are opened, the full 72" of glass area is completely open and the views are unobstructed.
This made a very nice focal point for the room and brought warmth to the room as well.