We made our own pattern. Use a 45" piece of fabric 1" longer at the top & whatever hem you want longer at the bottom. Make one seam at the selvage as the center back seam. Fold the piece flat with that seam in the back. There will be no side seams & you have a fold there. Make a template approximately 1 1/2" x 5". Curve one corner starting 1" in & 1" up the side. You can use a glass to aid you. Place the longest straight edge on the fold of each side & cut out armholes. Face these armholes with bias tape.
You have 2 straight edges at the top, turn these down 1" & hem for casings for ribbon. Once you gather this edge up, secure the ribbon to the fabric with a few hand stitches to keep it in place. Hem your bottom.

This template works on about a 2-5 or 6. You can make it shorter or longer for other sizes. Most of the fit comes from gathering the ribbons at the neck & how much excess ribbon you use when tying. You can raise or lower the armhole then. We use from 1 to 1 1/4 yds of ribbon on each side. We have seen one longer piece used all way around & tied on one side too.

If you use these for jumpers, you must use a feminine cut of a T shirt or a blouse. Unisex shirts or oversize, off shoulders have sleeves that drop too low. They just bunch up & won't let the armhole of the dress hang right at all.