Measure inside of window frame, and use dimensions to cut one piece of ticking and one of linen.
Place right sides together; pin along sides. Cut three 4-inch lengths of twill tape for loops.
Fold ticking and linen outward 1/2 inch along the bottom, and press.
Position loops on ticking fold, one at center and at each corner; machine-stitch back and forth to reinforce.
Leaving a 1/2-inch seam allowance, sew up the shade's two sides.
Turn right side out. Draw out loops; sew bottom shut.
To finish top opening: Fold linen and ticking inward 1/2 inch; press, and sew closed 1/4 inch from edge.
For curtain-rod channel, make a second seam across top, 1 1/2 inches from the first. Open channel's side seams with a seam ripper. Place two rows of buttons -- three at the top and three halfway down the shade -- so they align with loops, and hand-sew them on.