I "learned" how to make a sweatshirt jacket verbally from one of the gals in the Plano guild. She always wears a cute jacket to our meetings, most of them are fabric pieces sewn on to the sweatshirt with the raw edges loose so they have all frayed edges. I wanted something a little more finished, so here is what I did. (Please note there is a lot of "winging it" in this process.)
1. Use a slightly large sweatshirt. You are going to cut off the seams and then sew all the pieces back together, so you need to allow enough fabric to do that. I picked up a cheap one at Academy.
2. Cut off the ribbing on the neck, cuffs and waist. Cut as close to the seam as you can.
3. Turn the sweatshirt inside out. Cut the the seam that runs up the side, all the way down the sleeve.
4. Cut the sleeves off the jacket. Be sure to mark which sleeve is right and which is left. (I didn't and I had a heck of a time figuring out which was which after they were quilted.)
5. Cut the front of the sweatshirt down the center. To figure out where the center was, I folded the front in half down the center and cut the resulting fold line off with my rotary cutter.

6. Now comes the fun part! Piece together whatever type of quilt blocks you want on your jacket. For mine, I sewed all my fabrics together in a square like a quilt top, used spray adhesive to attach it to the jacket and then cut the quilt fabric out using the sweatshirt as a "pattern". Alternatively, you could use a "quilt-as-you-go" method. Sew a piece of fabric to the sweatshirt, fold it over and press it, then sew the next piece

of fabric on. Here is a picture of the inside and outside of the jacket "core" after I quilted my fabric on it:
On the top where the blocks are, I quilted a "grid" on the diagonals so there is an "X" sewn through each block. On the bottom where the kids are, I quilted around each kid, then did some free-motion on the black background.

7. Then I did the same thing with my sleeves. I had planned to put some more of the patches along the cuffs of the sleeves, but Mom pointed out that it would be too busy. After looking at it for a while, I decided she was right. So my sleeve is just one piece of fabric, quilted in a 1 1/4" grid.
8. Once all the pieces are made, it is time to sew the thing back together

again. This is a bit tricky, as now there is not as much "stretch" to your sweatshirt. Sew the sleeves to the core, then sew the seam up the side and across the bottom of the sleeve. I used a walking foot to sew the initial seam. After I sewed the seam, I went back and zigzagged the edges. (Or you could serge them.)
9. When the jacket is back together, bind the edges. It probably would have worked better if I had cut my binding on the bias, but I only had a little bit of the red fabric I chose and it completely slipped my mind until after I had cut the strips. My binding was 2" wide. I sewed several lengths together to make a long piece then ironed it in half lengthwise. I sewed my binding on the right side of the quilt, folded it under and sewed along the binding edge on the outside (catching the bottom in the seam).

Here is the jacket, almost done. I need to finish the cuffs, but I think I will use some scrap batting to make these sleeves a little longer. Got to get this done to wear to the quilt show!