Heyhey, so here you can see how I started with that pattern for my vests/waistcoats and how I changed it for different garments:
First you need to measure from your shoulder to your chest and from your chest to the point you want your vest to go, mine was almost to the hip. So you take a paper and go on the edge of the paper up from the point you marked as the length the measurement to the chest and from there chest to shoulder.
from that chest-point on the paper-edge go in a right angle 1/4 chest + 1cm
from there you go in a right angle back down to the line where you started… thats your hem-line
from the shoulder-point go in a right angle 1/4 neck
then go from that new shoulder line in a right angle down and from the chest a quarter circle up and then connect them with a curved line and your pattern is finished. Now you need to get your front and back part and the collar.
draw the pattern on another paper, add seam allowance at neck, shoulder and side and cut it
draw the pattern on again, this time go down at least 4 cm in the middle of the neck and also make the arm-hole a little bigger (about 1 cm)
go down at least 2 more (2 -4) cm from the shoulder point and cut it. For the front-part only add seam allowance at the neck and cut it
now measure your neck-hole (the red line) and put it on another paper as a straight line. At one side go up 14 cm in a right angle at the other side in a bigger angle.
connect those 2 points with a curved line and draw a line in the middle, you cut that line and glue both parts on another paper and split them by 14 cm. Then reconnect the down line a curve. Do not add any seam allowance at the collar-part and cut it.
draw the neckline into the middle front and draw a little down from the line you drew before and cut it.
draw the back on another paper, too. then put the front part on it and make sure the side-seams have the same length. then draw a line at a right angle from that side seam length. and cut it.