Having given this some thought I am wondering, do you really want to use a thin veneer on a customers build?
Thin veneers can be difficult to glue down without a vacuum bag and also they can "creep", leaving either a gap or the flames not matching correctly.
Another potential problem is unless you are binding the Guitar, a thin veneer will cheapen the look and also may lift around the edge.
So, IMHO, it probably would be better all round to use a thicker top of 3-5mm as this will circumvent the above mentioned potential dramas.
Sure, it will cost around the $200 mark for a master grade top but on a custom build it is worth the outlay.
I also must agree with the Bman, that body has a beauty all of its own and it would be a pity to cover it.