Might I refer you first to www.ffurg.com
which is THE
first and foremost customizing resource website. It's also my 2nd home basically.
They have some griming up articles that should help you out under drybrushing or painting techniques I'm sure.
The issue of scratch building droids is a fun one, because youc an simply take various pieces of plastic, and if you have a knack for it you can slap them together and make an interesting droid.
For instance, the yellow droid that came with the one E1 accessory pack makes a nice base for droid customs. Also the "Battle Bots" figures which MisterPL says are being clearanced at TRU's now, are good possible custom droid fodder out there for low low prices.
Now, as for spacing out the legs of a protocol droid, that's tough... The 3po figures have spaced out legs already for the most part, is that what you're using?
The plastic used on most 3PO figures (not all though) is rigid, so spacing the legs apart won't really work without breaking them, sad to say.
But protocol droids tend not to stand with their legs apart either. Check out 4-LOM even, as his legs are pretty close together. Probably a complication of the costume because Anthony Daniels and all the other bi-pedal droids seem to have their legs together tight as well, and the costumes probably don't lend themselves to be very flexible.