Here is a picture of a t-shirt quilt.

T-shirts can be arranged symetrical like the above picture or randomly like the bottom picture.
Close up of quilt. This quilt has a lofty polyester batting. Quilts can be made with a flat cotton blend batting for a different look.

When one of the t-shirt is smaller than others or the design extends up around the neck, the neckline can be preserved and the back of the shirt is used and forms a little pocket.

Close up of quilt edge.

Another close up. T-shirt scraps were used here to create the binding edge on the quilt.