I used 17" square pillow cases so my measurements are based off of that. If you have different size pillows check out my basic pillow case tutorial for info about how to get the measurements for different sizes and add 11 inches to whatever you need.
For a 17" pillow you'll need 28" of fabric (by the width probably 44" or 60").
For a 17" pillow case you'll need fabric cut to 17x38 (pillow case), 9-11x38 (bow), 6x6 (bow tie). My red pillow case I used the 11x38 inch bow and the pink one was a 9x 38 inch bow.
First sew the bow. Fold the bow piece in half so that it's 11x 19 and sew the long sides. Flip it right side out and iron.
Make the bow tie. Fold the 6x6 piece in half and sew around three edges. Flip right side out and iron. Tuck one end into the other to make a little tube (like a napkin ring kind of) and fold under the edge of the top layer and sew shut. I had to sew from one edge to the middle cut it and sew from the other edge to the middle.
Finish the short edges of the pillow case piece. I did this with a serger or you can just fold the fabric under twice and sew.