I came across this book on just such a topic and since it's short, I gave it a try. Having done zero quilting in my life, I mostly wanted to see if this kind of project was beyond my skill level.
The first 20 pages or so briefly discuss the methods you should use for a t-shirt quilt. This book specifically states that its goal is not to teach quilting, but merely to illustrate methods for using t-shirts. Whomp whomp. But really, that's okay, because I'm not in the mood for a quilting project right now anyway and I'd forget anything specific.
The book did cover interfacing, which was something I wondered about. It also contained tips on piecing and color theory.
The remainder of the book gave examples of t-shirt quilts. Patterns, I guess? You can tell I don't know anything about quilts!
One thing this book emphasized is the addition of regular quilting cottons into the designs. I'm not sure if that's something I'd like to do. There is literally a line "you can never have too much fabric!" which I would disagree with, as an apparel sewist and in apparel you definitely can have too many fabrics in one design!
Have you ever made a t-shirt quilt? Or found a better resource than this one? I'm all ears!