Once upon a time I had this lovely jumper, which got an un-lovely hole in the elbow.
So I felted it in a nice hot wash, cut on the dotted lines (as shown)
and sewed it into a delightful cat bed. (She sleeps on all my jumpers, might as well give her one that's hers alone!)
Here's a view from the top. I cut pieces 1 and 2 out then whipstitched them together. The sleeves are folded over for more stability.