Hey Rebecca,
This the the method I use:
1)Trace the shorts pattern out leaving large section on bottom for adding length.
2)Draw a straight line down from the bottom edge of the hem on the crotch side of the pattern the length you want. Let’s say it’s 3 inches. Draw a line down, straight, 3″ and do the same on the other side.(It’s the straight side of the pattern piece)
3)With a long ruler, line it up with the crotch curve edge and the bottom of the 3″ line you just drew. Draw a new line.
You’ll notice the little indent from the pattern hem line and the 3″ straight line you drew is now incorporated into one long slightly angled line.
4)You’ve already added 3″ to the other side so simply draw a line across to mark the hem.
5) Voila! Lengthened shorts.
~Deb~