How big could my finished poster be?
Your poster could be 54” x as long as you want it to be.
What should I consider when designing a “Large Format Poster”?
First the resolution of the imagery that you plan on using. If you're working with a web graphic it’s probably not high enough resolution to produce a 24”x36” Poster with. The image should be a minimum resolution of 300dpi at a size of 8.5”x11”. Consider how close your intended audience will be to the printed piece when viewing.
What type of use should I consider when producing a “Large Format Poster”?
This type of product is typically meant for short term indoor or outdoor use and is not meant to handle weather. There are different types of materials that can be chosen to compensate for weather or constant direct sunshine.