The BUILDING.md is a markdown file that people can immediately review, although it's references are dated (seriously, who still uses Qt5.7?). It could use some clean up. The file is available with cloning the repository.

The WIKI is the canonical resource. People who would do packaging for different distributions (SUSE, Red Hat, Arch, et al) would want to look here for exact details along with any pitfalls/considerations.

However, each should refer to the other. The existence of these resources need to be current but separate as they serve different use cases.

My $/€/£/¥ 0.02 worth.

Yeah, having stuff on the wiki is a good idea. Like @scottfurry mentions though, having info for that specific release that's in the release itself is also useful.

One problem with wiki documentation is that it's generally targeted to the latest source code. So, if some major change in build process happens then when the wiki docs get updated it won't be accurate for the older releases.

At least, not without having separate pages. "For release 0.1.0, go HERE. For release 0.5.0, go THERE, etc".

Wiki pages are much easier to update than creating PRs for documentation changes though. 😄