Just to add to the two responses above...Find someone with a high quality solvent printer. Mutoh and Mimaki both make high resolution "EcoSolvent" and "MildSolvent" printers. These printers can print on paper, but they do a great job of printing directly on high end vinyl material, which might be best when hung in direct sunlight.
Remember that even these higher end solvent banner printers do not print as well as an Epson if you want to view the prints at really close range. The motto of grand format printing is "Backup and Shutup".