To make the shirt front pattern, lay a custom doll sloper, folded in half along the center seam line, over a large piece of paper and copy the neck, center front, shoulder, and arm hole lines from the sloper onto the paper. Draw a line at least 1/8 inch above the neck and armhole lines to mark the seam allowances. For your first shirt, where you aren't used to working with smaller scales and fabrics, move the shoulder seam up 1/8 of an inch above the line marked on your sloper, then add a seam allowance. As you test fit your shirt, you can always adjust the shoulder seam to move the shirt up the doll's body. When you sew seams in fabric, the thickness of the fabric and the seam will hold the shirt higher up the doll's body than your sloper was designed for. Your sloper is the 'skin' of the doll and the shirt will have to be larger to fit over the skin. Most seam allowances are shown in red on the photo above.
You will adjust the armhole lines in the next step, so don't cut your pattern free from the paper yet! Mark the length of the shirt front below the waist onto the paper, making sure you add extra fabric to allow you to turn up the edge and finish it neatly (allow an extra 1/4 of an inch in most cases, below the length you want your shirt to be).
Determine how tightly you want the shirt to fit, and add at least the width of a seam line to the side edge of the underarm on your sloper. Most loose fitting shirts can be adjusted on the side back to the outer edge of the side bust dart line on the sloper. Draw a side seam line down along the points from your extended underarm at the top of the side front of the shirt, to the bottom hem line of your shirt. Draw another line at least 1/8 inch outside of that line to mark the seam allowance.
Determine how you want the bands or center front edges on your shirt to overlap. Most shirts will have a slight overlap to allow for buttons or snaps. On smaller doll shirts you can sewn on tiny bits of velcro for shirt closures and sew the buttons to the outer visible layer of the shirt for show. Leave at least 1/4 inch of fabric (for most doll shirts) on the outside of the center seam line you transferred from your sloper pattern, to allow you to turn over and finish the edge of the shirt along the center front.