ResizerBot - Parametric MakerBot-Setup

I was thinking about the optimal stage set up for the MakerBot to increase the maximum buildable area. This is the outcome:

My idea: Creating the whole stage from one big extruded/casted (aluminum?) piece, just adding a motor, a belt and rails. If that actually works, what about using the same pieces for all three stages? Wouldn't that be awesome? It could be quite precise and very, very cheap to produce!

What do you think?

Best of all: This design is size independent - the base, belts