There have been several postings for linking sheet metal cut list properties to custom properties, specifically bounding box area, length and width for this post.
It's my understanding there's no direct linkage available to connect a cut list property to a custom property which can be used outboard of the note linked to a flat pattern drawing view.
I've previously tried creating global variables for the length and width using the measure option, but this method didn't survive part alterations.
The dimensions remained in Manage Equations but were not available for re-attaching to the bounding box.
The attached uses a sketch (just lines with only endpoint constraints) from which a surface extrude was created then hidden. I added the extrude to try to make this method "more permanent" compared to the global variable/measure method.
If the sketch gets disconnected from the bounding box, it remains and throws a modeling error, which is evident and is readily fixed with new endpoint coincident relations.
So, if you're interested, please review the attached and see if it's robust enough that it can be of value for those needing these data.
Your collective wisdom will be most appreciated.
Thanks and cheers,