Does anyone build GrapheneOS "from scratch"?

I'm wondering what would be necessary to build GrapheneOS releases yourself, and regularly update your phone from your own servers, with your builds. The server for apps.grapheneos.org should also be replaced. Has anyone done this?

The documentation for GrapheneOS has a section about how to reproduce builds:

https://grapheneos.org/build#reproducible-builds

But it would be more involved than that.