Here is a super quick and easy way to make a curtain for any window.
I needed one when my old house was on the market so I could get rid of some hideous shutters.
First, measure your windows width and length.
Second, find a piece of fabric that is big enough and matches your decor.
Third, cut one large rectangle to the measurements you took adding a 1/4 inch to each side for hem, and 1 1/2 inches extra on the top.
Fourth, with an iron press your seams over twice and show (do not to top seam yet)
Fifth, roll your top edge down once 1/4 inch, then again over one full inch. Sew right across so you have a tube at the top.
Sixth, sew at the very top of your tube 1/4 inch down. This will create a nice ruffle on top.
Lastly, insert your rod into your curtain tube on top and put up in your window!