Bukkit

What is the enhancement in mind? How should it look and feel?
I am thinking that you could reuse the Planter code for this one.

You could have a row of chests that depict the layers that will be built.
And the till arm can be longer to accommodate the layers.

An example of things that could be built would be the Drills, Builders, Hoverpads and in the case of other mods like the one http://dev.bukkit.org/server-mods/ships/ -- ships.

Then via redstone bridges and other circuitry an enterprising minecraftian could create an automated factory that built objects on demand for customers.