there are printers that print big enough to produce bike panniers - but they're commercial machines and not cheap.
The other thing to bear in mind is that you'll need to design or get designed the file used to print the part.

Printing stuff is the fun, easy bit. Designing the actual part is the long and harder part of the process.

It's fun if you're that way inclined. Just bear in mind that you can't just point the printer at something and say: 'make me that in green'.
Not yet anyway - give it a few years.


What sort of maximum dimensions are you thinking about ?