The underwear and the "hammam outfit" too
Back to the question, as Forsaken said, depends. Sometimes it's also something put together at same time, like with Loren, beside the basic plot outline I had already decided some main cast characters: Loren, Karen, the player, and Apolimesho. Sometimes new characters gets added along the road, or their personality changed a lot.
Rowinda from SOTW for example was just supposed to pretend to be mad. Then, after reading how fun it was, I told the writer to keep her crazy for real!!!