Here I've quickly slapped together a model with the proportions I want using many primitive spheres and cylinders. I'm retoplogizing it in order to get a base mesh to bring into zbrush.This method works great for quickly building new characters with the forms you want in mere minutes, and also for retoplogizing a high-poly sculpt to make the game-ready mesh.
Quick Snap method:
1. Place reference model in new layer, disable the ability to select it.
2. Right-click your snapping filters, and make sure surface is enabled and on.
3. Begin drawing your new model over-top the surface using snap. You can also transform verts, and they will snap to the surface as you move them.
1. Apply a shrink-wrap deform (Modify>Deform>Shrink Wrap). Select Closest Surface.
2. Open the modeling stack and move Shrink Wrap to the top. Now it will be the last thing applied, so Shrink Wrap will be applied automatically to new verts, loop extrudes, etc.
And finally here's a video showing both methods in action.