I don't think you need to follow hard and fast rules for NPC droids. Make them how you need them to fit plot, add a little flair, and you're done. As GM, you don't need to belabor the build, just assign some stats and move on.
I of course will be in the front of the line to buy a droids book, certainly! Until then, I've gotten pretty far with a copy of The Essential Guide to Droids and flat out making things up.