Well, for a nice print you would need the resolution at least 200 pizels per inch. That will lead you rendering a 12000x7200 pixel image. Anything less and you would be able to see the pixels in the print. Because this is a large format "visualization" scene, you could charge quite a bit of money. I would say 30 dollars per hour plus printing. (printing will be very expensive at that size) I would do a "preview" render at about 1700 pixels x 1020 pixels. Then when the client is happy with that, crank the resolution up to 12000 x 7200 pixels and render to disk. CAREFUL!!!! DO NOT USE PHOTO TEXTURES UNLESS THEY ARE VERY HIGH RESOLUTION! Using a low res phot texture will look fine at web size, but i will look absolutely aweful at large format sizes.