The dress I made is for a 12 month old. Of course, you can always use a pillowcase, since it's where the name came from, but I used fabric.
1. Cut fabric to approx 16" in length and 30" wide.
2. With right sides facing together, sew side seam and then iron open.
5. To finish the top, I pressed under 1/4" and then folded under 1" and sew.
6. Cut ribbon into pieces about 1 yard each and feed it thru the pockets you just made. You may need to cut them a little shorter, but wait until you try it on the little one first. Use a little fray-check on the edges of the ribbon.
7. You could just fold the bottom under 2 or 3 inches and sew, but I decided to add a contrasting border. I cut a 6" piece of fabric 32". I folded it in half to create a 3" border on the dress. Press each raw edge under 1/4" and sew into place. You can also add ric rac at the border - I'm still considering it.