One of my favourite tops!
I made this out of a jumper that was too small for me. The neck is from the textured cuff, but could be made of matching material I guess.
Measure body of your pullip around the hips and the length of the torso. Cut a square a little bigger than this (for the seam and optional hem)
Then cut a square that will fit around the shoulders and fold two or there times to cover the upper arms.