I bought a curtain in the clearance section at Home Sense for $10
The shades are not drum shaped, they are slightly tapered at the top. I placed the shade on some kraft paper and traced it to create my pattern.
I cut it out 1/2” bigger all around to allow for seam allowance. I then traced it on to my fabric and cut them out.
Turn the top and bottom edges over 1/2” and iron, then sew.
Right side facing in, wrap the fabric around the shade, brining the ends together, then pin down the length of the fabric.
Remove the slipcover and sew down the edge that you marked with your pins.
Turn it right side out matching your seam to the seam on the shade, and slip it over.
That’s it. Easy to do and easy to change.