Nerdipedia documented a 3D printer build, called Huey:
This is not a general purpose 3D printer. It is the size of a small chest freezer and has a expected build volume over 200 litres. It uses eight drive motors and may require a lot of setting up compared to printrbot or similar.
The parts are mostly printed on my printrbot.
Unlike most repraps Huey has a stationary bed. Therefor the printhead must move in X,Y and Z dimensions.
Provided motors have enough motor torque and power this should scale up to be even larger.
You can find the build log here.
Check out the video after the break.
I thought that the effects of plastic shrinkage from deposition temp. to room temp meant that any part much over 20 cm long will break off the build platform due to stress buildup. I guess not if you keep the bed hot enough to keep everything a bit soft (?)