1. Go to the nearest charity shop and buy a few men's shirts, size won't matter.
2. Buy a new or second hand sewing machine and get a hemming foot for it.
3. Practice, practice, practice.... until you can re-hem a shirt to the desired length. If they are too wide at the waist, then learn how to take them in to the desired size.
All instructions are available on YouTube and ask on the sewing section of the forum if you have any questions.
Oh, and if you can hem and seam, you can make your own skirts too.....