|Georgene is the one who is the brains behind this tip. I had asked her for advice on adding a cuff to a pants pattern and this is what she wrote to me:
"If you are going to do a 'straight up' turn back cuff, yes you would have to add double the amount of what you want to see as the turn back. Ususally the actual hem part on the inside is not as wide as the amount of the cuff, so double check how much your hemming allowance is.
Tack your turn back at the side seams, and if your fabric is heavy or very drapey, you may want to use a running stitch about 1/" below the upper fold of the cuff to hold it in place so it doesn't droop. "
It worked very well for me.