The single biggest prints I have actually done were 6' high by 18' long.
These were colour prints using Kodak colour EP2 paper followed by RA4 paper when it came out.
The paper came in 100' rolls, with a few rolls to a container, which looked like a smallish coffin.
The processor we used was 76" wide, trust me when I say that loading a 20' to 22' roll of 6' wide paper and hopefully getting it straight was interesting.
Every now and again you could hear the gears that drive the rollers making a funny noise, this meant the paper had tracked sideways and you hoped that the tracking wouldn't get that bad that the machine stopped, or the paper started to jam and then slip and be scratched by all the rollers over the length of the print.
Pulling a piece (or pieces) of paper that big out of a roller transport machine that big, could sometimes take an hour or more to sort out, plus there was the wasted paper, which wasn't cheap.
Working in total darkness with another person and using retractable bladed knives to cut paper whilst one person held the pulled out part of the roll, whilst trying not to kink it, was another excercise in gymnastics.
The end product was, at the maximum, a single colour print on photographic paper, as you would use in your own darkroom that was trimmed down to 6' high by 18' wide. Which for the rest of the world except the Americans and the British, is a print that is 1.82m high by 5.48m wide.
With B&W paper the biggest we used was rolls of Ilford paper, this was 48" wide by, I seem to remember, 100'. We used a bank of enlargers in our B&W darkroom all equipped with Ilford multigrade heads, which were absolutely fantastic. To be able to change the filtration whilst exposure was happening was a useful tool for doing very fine bridal veils and things like that.
We sometimes used B&W paper in our mural darkrooms, the biggest we could do were 4' high by 22' long, but this was only with a 4x5" negative, if we used our normal 8x10 negative, then the maximum size was 19' long. The restriction was there because the longer lens required for the larger negative, restricted the enlargement factor.
Going from memory here, but the only photographic paper over 4' wide in rolls, was manufactured by Kodak, and this was colour negative paper only. Their reversal papers were 4' wide, I seem to remember that Duratrans was only 4' wide as well.
Nothing I ever saw from Ilford was wider than 4'.
I do seem to remember that there was one Drupa exhibition in Germany whereby Konica, Agfa, Ilford, Fuji and Kodak or an assortment of manufacturers like that, got together to manufacture the worlds largest single print. I believe the end product was a huge single print, which was literally billboard size.
This was either in the very late seventies or in the eighties. For those who don't know what Drupa is, it is the worlds largest printing exhibition. Held every four years at Messe Düsseldorf, it made Photokina look like a chook raffle, sort of