I’m classing mine as built lol. I do all the work myself apart from building the engine but at the numbers I’m after that’s a very specialist job. I’ll fit it and I’ve done everything else. But some people don’t have the ability or room to work on there own cars. As long as you have been involved and interested in what’s actually gone on what dose it really matter.
Cars have many very specialist areas like paint and body. Heavily tuned engines. Mapping. Transmission. Suspension set ups. Fabrication. Definitely not always possible to do everything your self to a high standard. Obviously there is the odd few out that but many more who just think they can lol