For our office, we have a separate plan that shows the extents of the shear walls. Typically we've done this in two ways.
1. Use a boxed text, with arrows pointing to the end of the shear wall. The text will float somewhere in between, but this causes problems during revision, because the location of text can easily get messy.
2. Use dimensions with text override. This auto adjusts, but anytime the endpoints change, I have to re-input the text, as Revit jumps back to the dimension and loses the text override.
I was thinking that there could be a line-based family solution, but I just wanted to see what other people are using.