For my first go at making this pillowcase dress, I decided to use the fat-quarter pattern I found on The Mother Huddle. I was able to figure the size based on inches and went from there. For the neckline, instead of an elastic neckline, I used a bias, that I made myself.
You could purchase bias tape in all sorts of colors to match your fabric, or you could make your own. Cut 2 strips of bias tape 2" wide and 13" long, fold the strips in half lengthwise and press. Open back up and fold both sides in towards the middle, then fold in half. Press with iron.
I loved making this dress, and I look forward to making more!