I personally sketch, scan, and outline the fonts I make. If it were something in the Sans family, I would only start with an existing font if I wanted to change that font slightly, not all together. Personally I always ether start with a blank piece of paper or a blank document. My favorite thing to do, actually, is draw strange fonts on odd objects, like dirt or wax, or in ink and blood on wood and what-nots, then photograph them, import them into FontLab and outline their images.