If you are running belly heat they would need to be fixed position. Also if a snake wormed it's way into a crack an slid a shelf out? might be above to move levels.

Besides saving some materials, what other benefit would this have over just creating individual cages and stacking them. A rack 4' wide and even a few levels tall is very heavy. What easy to clean material would you use for these racks , since the snakes would be on them directly?

Just a few thoughts