In the early 1900s, when automobiles were exclusive to the wealthy, this type of work was not uncommon. Automakers sold frames and engines, and specialized design firms completed the exterior.
In a time when the automobile industry was not mature, the process of making cars and wagons was a similar process. So, in the transition period, Coachbuilder and Carrozzeria, who specialized in covering the exterior of the frame like this, flourished. The two are words that refer to the same thing, and the only difference is between English and Italian.