if the image is 300 dpi then you can have the image, like stav says if crisp etc... as big as you could wish....

a normal roll of canvas would be a width of 2 meters x miles....

if this is for your hallway i would imagine the biggest you would want would be 1.5m x 1.5m

i can get this done for you if you supply image mate and size.
will be on a canvas stretcher too (frame).