On one piece of paper or as a photo mural? Largest paper available today is roll paper that comes 48-inches wide by xxx feet long (I forget the number of feet). So, you are limited in one dimension by the 48-inch width.
What would be interesting to do, is stitch together several (like 3) panoramic format photos & have them output on a LightJet as it has a roll of 48-inch wide paper loaded in it, and should be able to print the entire length of the stitched together photo ....
Oooooooowww...that shouldn't be too expensive!!
Look at the big stuff done by Chuck Close. AND, do assemblages like those done by Robert Raushenberg count?