There are dozens of ways to customize cutoffs. DOZENS!
Start off by cutting a basic pair of shorts.
Here's everything you need to know about making cutoffs that won't cause chronic underbutt, unless of, course, that's the look you're going for.
Source: refinery29.com
You can also make them with a high-low hem.
Source: swellmayde.com
Now that you've got your simple pair of jorts, THE WORLD IS YOUR DENIM OYSTER.