You could always make a drop shoulder sweater...knitted straight up to the shoulder shaping, mark where you want the armholes to begin (no worry about armhole or sleeve cap shaping). And with the sleeves, you could even pick up the stitches around the armholes and knit from the top down. Would be an easy first sweater, imho.
Ack, just reread your post and you want to make a vest...that you'll have to shape the armholes. If you need directions, I can get my Vogue book out and give you the formula they give for shaping armholes.