The Image above is by Bay Decorators.
“Railroad” the fabric (use the width of the fabric for the length). That will give about 52 inches for the length. If the window is longer than 52 inches, an additional fabric can be added and seamed together. That will work with hobbled Roman shades and the flat Roman shades with bar inserts. In this case, the seams can be easily hidden and the finished product will look clean and elegant.