After a failed search all over the web for directions on how to make an adult sized pillowcase top, I took the advice of a fellow crafty nestie decided to somewhat wing it.
Basically I used my bust measurement and added 3 inches for the width. I used 26 inches for the length. Please excuse the horrible pictures. I really need to have DH help me take better ones. The pictures do not do it justice. For a non-maternity shirt I would probably experiment with making the back slightly smaller than the front.