Most building is concentrated in the migration destinations. You can find the breakout on the FRED website for different metro areas.

I would be particularly concerned about sustainability of prices for places like Boise or Phoenix. Lots of building there, and prices are far detached from local median wage.

Also lots of land and few regulations preventing further building.

Phoenix was one of the places hit hard in GFC. Prices fell 50-70%

Are people making that move because they prefer the location if their current location had enough housing? I guess more "Are they moving b/c the building is happening there and not in CA?".