They don't really need a huge amount of height, floor space is what really matters. The only time height is really a concern is if the heat lamp is build into the cage. Many people suggest a 4 x 2 x 2 foot cage for beardies.
Here is a cage I just set up for mine (its an Animal Plastics T12 (4 x 2 x 2)
Full Specs here: http://ball-pythons.net/forums/showt...n-Interim-Cage
I started out with a 20 gallon long tank
So 23 3/4 height should be perfect.