The only real artwork requirement is High Resolution. I will print what you send, just keep in mind that a 2" 72 dpi image from the web blown up to 50" will be very pixellated. As I tell all my clients, please send me the artwork straight from the graphic artist, in the format they created it in. AI, CDR, FS, INDD, PS, EPS, PDF, SVG, CPT formats are best, but not required. Or low compression raster formats such as TIF, BMP, RAW, JPG. Most of all I would like the original artwork unconverted from the program it was created in! Do not export it with anti-aliasing turned on, it will create faint lines in you print.
Ideally, but not required, the size of your seamless pattern should be 12"x12" art board/page size, and double check that the pattern matches up on all four sides.