In order to fit the final shirt into a quarter page envelope, choose a piece of paper 10 inches long by 7 1/2 inches wide (or less). Fold in half lengthwise then fold both sides to middle.
This will be a little shirt that you can attach to a greeting card. Start with a square piece of paper. Perhaps 2 x 2, 3 x 3 or 4 x 4 inches. Fold it in half, then fold the sides in to center.
Next bend the bottom up to the back. Make collar by bending the little flaps in front.
Turn over to back and bend triangle as shown. These will be sleeves when turned over.
Finally add buttons, pocket or whatever you want. You can cut a curve in the neck opening.