The best thing to do is mock it up, and test it.
My guess would be around 36-37" at the front, and 37-38" at the back.
The most important factor to me is not the height, but rather the angle of the CP.
I've played a few people's home-builts that had the CP angled too sharply.
On those, your wrists have to bend too far, or you have to lean over too far, to make them comfortable while playing.