I think any space you add will benefit your snakes, but ask yourself the same question: Would you make use of the space? I say add the extra foot in height. 3' is a much more workable height than 2'. You could store things on top (assuming lighting is inside). Heck you could even buy a piece of formica counter top to go on it (about 26" wide, to match your 24" width). How will you utilize that 1' of wall space if you go shorter? You probably won't do more than hang a poster there. Another thing you could do is buy some nice big castors (wheels) so you can move the monsterous cage easily for cleaning and stuff. This will also increase the height. Remember to make it so it can be moved thru all doors and make turns. 8' is really long; I'm currently building one the same length. You might consider building it in two pieces that combine to make one big cage. You could even make a partician that would allow you to leave snakes in half while removing the other half for cleaning/repairs. Or it could be a shift allowing you to introduce food while the snake is isolated from you, greatly reducing the risk of being bitten. Just a few suggestions.
Good luck,
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Zoodude
1.1 Acrantophis dumerli
0.1 Python molurus bivittatus
0.0.1 Morelia veridis
1.1 Elaphe (panthertophis?) obsoleta lindheimeri
0.2 Bogertophis subocularis
1.0 Pogona henrylawsoni
0.1 Geochelone carbonaria
3.2.1 Phelsuma laticaudal laticauda
1.5.1 Eublepharus macularius
0.0.1 Lampropeltis gutulus hobrooki
2.1.12 Elaphe guttata guttata