use a top as pattern.
just fold it up, and draw around it.
there is gonna be a seam down the back, so you'll need four pieces. 2x front, and 2x back pieces.

on the front pieces the neck line is to be lower than on the back pieces.
draw it the way you want to. a good idea is not to cut it too low at the beginning. you san easy cut more off later, when you have tried it on.

when ypu have cut all the parts out, it should look something like this.
i allways make my patterns way too long, guess i like the safety, but you dont need to do that.

needle the parts together, and sew the edges on a machine.

now you have a chance to try the vest on.
cut the armholes, the neck line, and the length as you want to.

now you need to make the hoodie, i used an old t-shit. (euo size xl)
cut it first, as on the picture, and then cut the buttom, so the original t-shirt stitching no longer eksist.

turn it inside out, and sew the two longest edges together (the once you cut first)

put the hoodie on to the vest, and sew them together too.

thats it!