Romans

Motorized Window Treatments - if motorized you must know to add wiring

Curtains (make sure you have room above to mount hardware

Shutters (heights, boxes, can they open, window crank thing

It is good in advance to know how much fabric you will need.

The window treatment hardware, romans or shutters should not be ordered until window casings are in. At times rods can be shortened on site at installation, I try and avoid telescope rods.