Start from a basic block with darts, draw the french dart on front and the style lines for the hem and back opening.

Close the shoulder dart on front and make a copy of it so you have the whole front (left+right).

Draw the hem and collar lines of right front.

Make a copy of it tracing the collar separately (the red line you see is the roll line).

Draw the left front.

And trace a copy of it, this time the lapel is separate.

Mark a notch where you see the number 1 – the area between n.1 & n.2 is open for the other front to pass through.

This is the finished pattern and you can find here the way to assemble it.