G A Pilot answered:
You can do this, Martha, if you do any sewing at all. Pick a top pattern you like, make a paper front of the neckline from the shoulders a little lower than you would like the opening, fold in half, then mark and cut a neckline. Hold it up to you to see if it's what you want. Add ¼" for a seamline, then make a muslin. Good luck! Let me know how you do.