Batiks are beautiful but if you are going for one of those designs where the sweatshirt and the fabric shrink a bit batks won't shrink.
I have made two that I think are what you are talking about. Don't have a website because we did in in my wearables group but I can walk you thru it.?All of my directions will presume you are talking about the kind that shrinks a bit.
1/get a sweatshirt larger than what you normally wear. The higher the cotton percentage the more it will shrink.
2/ lay the sweatshirt out flat inside out and mark a line down the center front.
3/ sew a line with highly visible contrasting thread on either side of line you marked down center front. 1/4" on either side of front center mark or just the width of your presser foot. Do not cut.
4/ cut open up the sides and the length of the sleeves on the bottom seam.
5/ remove all ribbing and save.
6/ stay stitch neck--you may even want to use twill tape to stablize it.
7/ we used 7 different fabrics 1/4 yard each. There will be plenty left over.
8/cut the fabric in 4" wide strips
9/ then those strips into 4" x 4" squares
10/ then some of the squares in half for 2" by 4"
11/ some of those in half for 2" x 2"
***********or do all of them in a random design you like*************
12/ lay these out randomly on the sweatshirt--one section at a time is easiest. A friend of mine was going to use spray adheseive. I don't know the results.
13/ quilt over this in whatever manner you wish. do so with entire surface
14/ sew seams together with small seam--serger is great.
15/ baste ribbing to a scrap of material with large basting stitches
16/ throw all of this in the washer and dryer to shrink. This way scraps will have shrunk like the rest as will have ribbing but won't be distorted.
17/ cut up the center front and try for size.
18/Adjust sleeves and length as you wish
19/ reattach ribbing if you want or make bias strips from scraps and bind edges.
Hope this is where you were going.