It depends, lots of variation. Thinks like interior components (plastics, fabrics), seats, battery cells are often not made on site. Or sometimes its on site but by a supplier directly integrated in your factory. Some companies make the battery packs in different location then the cars. Sometimes electric motors are made of site as well.

One difference is that Tesla uses aluminum castings on a large scale. So they basically get raw aluminum melt it down and then cast it. But that is not so different the stamping parts locally.

The real difference will be in terms of batteries. Texas and Berlin both have battery cell production on site. In Texas its literally in the same building. No other manufacture has that yet as far as I am aware.

Tesla is also doing cathode and anode manufacturing in house. They seem to even be moving cathode materials production in house as well but I am not sure if that's already included in the current buildings.

I think Tesla Texas will be the most complete end to end car done in one building. Stamping, casting, plastics, seats, fabrics, glass, panting, battery cells, battery packs, motors and more besides in on big building. Thins that are still missing is of course computer chips, electronics.

If they actually do cathode materials manufacture there nobody else is even close.