I was tasked with cutting 4.5 ft. letters from double-wall cardboard. The monster-sized sheets I worked with were 76"x60". Since my laser bed is only 40"x24", I had to do these the old-fashioned way. I used my Tracer projector, a drywall ruler and a large utility knife.
Here are the letters in place at the KARM Store in Powell, TN. They're so large, you can see them from the front door.