Labels in sketchup do not have a dynamic link, they are static. The facearea formula can be used to report an area, if the area is altered via the size or scale, then a scaler DC needs to be bedded in the DC for this to work. If you alter the raw geometry inside the DC, then a simple redraw should update the attribute concerned, this can be triggered with a change to an option, or short cut to the dynamic component, redraw via the context menu.
The attached example has a scaler (thanks to Tig) embedded in a simple DC, the onclick does a redraw and an alert.
So the scaler updates any scale changes on the DC, whereas the onclick is the trigger for the report (redraw included)
You could modify this to report specific materials
area check.skp (99.8 KB)