I've made a lot of shapes, and while yes you can start by creating a new shape from scratch and moving the sliders, it can take a lot of time and a LOT of patience, because the shape isn't just the sum of the pieces. The pieces interact to make a whole, and this is especially true in the face.
It's a lot easier to start with a shape that is something like what you want; make a copy of it and start fixing it. There is a learning curve even to doing just that. Also, many little tweaks over weeks and months can add up. If you get to a point that you like, but want to go on tweaking, make a copy and give it a different name so you don't lose all the work you've put in.
If you take a part, like the breasts or nose, there are several sliders involved, and when I'm trying to get it right, I'll add or subtract 20 to the current value, to see exactly what the slider is affecting. Then I back it off by ten, then five, then two or three. When you see the big change that you're looking for, back down from that by two or three points, so it looks more natural.
Anyway, you might find exactly the shape you want in the marketplace, but if not, you can make your own. Just remember that it takes time and several sessions (if you're anything like me).