WoW theres an idea and a project!
could be anything...
he may want to be a demon, or some other supernatural entity.
he may want to be a cat or a dog,
he may want all over leather/rubber effect, (that would be something a naked, yet body painted rubber clad sub [such a juxtaposition])
but by head to toe....I assume he means a full body job, he wants to be effectively body painted.
but since he hasnt specified what exactly I assume hes leaving this up to you...
You may need to narrow this down a touch with him...
I think I would ask him:
If the ball has a theme,
if hes a sub or Dom, (this tends to effect the portrayal people go for)
if he has any accessories he wants/or would like to incorporate
and I would definitely enquire if he plans to wear any sort of underwear... If you are uncomfortable with this level of nudity you may wish to provide some sort of waist and below cover... (a loincloth or close fitting shorts of a suitable colour)
and how hes planning to get to the ball, because if hes wearing a cloak/coat or sitting in a car it could disrupt the effect.
you may find with a bit of prying he has some ideas (some maybe quite firm) about how he would like to appear.
(sorry I used to do some theatrical costuming and fancy dress costuming too, but never anything on this scale... but these sort of projects always fire my interest, if I can help at all feel free to PM me, and if not Id love to hear what you came up and how it went.
All the best,
U.