Build your own build system sounds like reinventing the wheel. As a former build build engineer and a nowadays devops, a custom build system would be enough for

Build your own build system sounds like reinventing the wheel. As a former build build engineer and a nowadays devops, a custom build system would be enough for me not to take a job. Because investing time to learn a custom build system is just wasted time, because you never going to use it again, on the next project or next job or whatever. Also for a project, a custom build system means, that you cannot hire anybody, who knows the build system, however if you are using any established build system, you can. And also, software developers tend to forget, that they are not the only users of a build system, and usually it needs to be integrated into a build&release pipeline.