Murals can be painted off-site on wood panels, Poly-tab fabric or canvas and then installed.  Designs can be also be digital and then printed and installed. Some of these options mean the mural is temporary. The life span of printed materials is generally much shorter than a mural painted directly on wall.  

If your mural is going to be designed and then printed – you could choose a graphic designer or digital artist instead of a muralist. Printing large murals can get expensive in additional to having it installed. So, it is not necessarily cheaper than paying an artist to paint a design. The image below is of 20 x 80 foot digital designs printed and installed on silos as a project by Emerging Terrain in Omaha.