Hi there, In this particular case, I would do the alteration at the end when you’re pinning the hemline. Have the person put on the garment. Pin up where you would like the hemline to be. In order to ensure that the hemline is even all the way around, you may be pinning up 1/2″ in the back but an 1″ in the front. The fact that you’re doing different measurements does not matter, as long as when the person is standing in profile, it looks even in the front and in the back. Once everything is pinned, you can trim the fabric that you turned under so that it’s all the same measurement. So in my case above, I would trim the fabric in the front part of the skirt from 1″ to 1/2″ so now it looks like a 1/2″ turned under all the way around. Then, just complete your hem as normal. Hope this helps.