Hi lanren - one possible way is to make a loft or sweep that has a large bulge in it initially, then draw in a line to cut off the bulged portion of it. That looks like this (also see attached 3DM file):



There I used Construct > Loft with the option for Loft style = "Loose", and for the boolean difference make sure to select the objects in the Right side viewport when you do the boolean so it will cut in that direction rather than vertically.

This will yield a very smooth body form since it comes from one surface, but the outline of the face is not controlled directly itself, it's a byproduct of the surface shape where it intersects the line, so you will need to manipulate the surface in order to get the top face into the shape you want.

If you draw in the curve for the top face to start with it will be much more difficult to get a nice smooth surface coming off of that.

If you find it difficult to manipulate the surface to get the proper face outline, you might try a hybrid approach where you do what I showed here to get most of the body but cut it off a bit lower and then connect it up to your drawn face outline by doing a blend between them.

Hope this helps!

- Michael