Depends on the complexity of the job.
Generally they get a drawing with measurements and callouts.
Then they gat a drawing on how I would like the monument to be
installed.
This
sign had a lot going on so I split up the measurements and the
specifications. From the 3 drawings, I got my engineering with no hassles.
If you don't have the experience you can get any number of designers
to help you, or they may have a stock solution. But generally, an engineer
only needs to know how tall, how wide, how deep, how it's installed,
what it's made of and what is it being mounted to.
I do my own drawings but you might try:
http://signmanmatt.com