I just completed the kitbashing of a Micro-Scale Models lighted billboard kit into a sign that appeared on the Weirton Steel 40" Blooming Mill exterior (and other places in the mill complex).
Here's the prototype (taken approximately 1957). The photo is courtesy of Weirton Area Museum and Cultural Center and used with permission.
The catwalk is stick-built using scale sized lumber from the kit.
Here's a good look at the billboard and catwalk (assembled). I used Microsoft Word to make the sign. It was glued onto a thin styrene backing sheet using a gluestick and then the catwalk was attached using Crazy Glue (CA).
Here's the mill with the sign powered by my K-Line PowerChief 120F transformer.
Thanks for looking!