Mine is bigger... I guess you know that one
Size matter... maybe that one too
The one you do not know is ... the bigger the size, the bigger the errors, hence... precision matters, and to obtain precision, the rep rap FDM models are out in space...
I can build you an FDM printer the size of a shipping container but...
If it is built by the standards to make it cheap, the output will be not commercial quality, and if I build it to make you classy cozy commercial quality output prints, than the printer will not be chap, at all.
Where lays the difference?
One thing is you cannot have shaking, belt dis-alignments, tooth skipping, belt elasticity, and precision in the same design. And what do the most FDM desk top size machines use? Belts. Why? Cheap, easy to work with, no engineering needed to study it.
On the other hand same size of a cheap FDM desktop, say 500 bucks ready to print, if you go ball screw motion powered, with encoder steppers, we talk 4 gran minimum, and the quality of the output goes up a lot, I mean some 200% or more.
Scale that to a cube the size of a 40Ft container, and you have belt technology on wheeled porters giving you a price of maybe 10 gran (just throwing numbers here) compared with ball screw technology that on a 6 meters length with 2.5 meters width might cost you 100 gran like nothing, plus assembling it.
How do I know that? Well, I am preparing to make me one, that is how.