I have tried to do that, but actually found that following the Klakar ship example (which is a photoshop file) loosely it the best solution. My Sphyrna race was drawn from scratch by first drawing a white outline and applying shading and color in layers over the top. Most of my ships for existing races were edited from fragments of other ships of that race, and my own contributions to filling in the gaps. For the additional tan ru and pirates, I scrubbed the color off the ships via a black hue layer and then applied colors or patterns over the top. And I have used photos for some things. But for making a whole race from scratch, i recommend following that file.
http://z7.invisionfree.com/SAIS_Foru...p?showtopic=98
There's the link.