In this Blender 2.8 tutorial I show you the new poly build additions for retopology that Pablo Dobarro added to the latest Experimental 2.81 build of Blender.
With a mesh snapped to the object that you want to retopo, the Poly Build tool is now able to add new geometry easily.
Edges get highlighted when the mouse cursor is near and then you can click to add new quads.
You can drag around vertices with the left mosue button pressed and press the control key to drag out new quads are triangles.
Poly build has an automerge option with a treshhold, so that vertices that are moved over other ones are merged together.
You can get the 2.81 version from this page:
See my social profiles here
Production Music courtesy of Epidemic Sound: http://www.epidemicsound.com