AUR is particularly useful because Arch has really simple build scripts. They are bash with some particular function names that you need to define (like "build" and "check") and a few bits of package metadata in variables. Pretty intelligible even if you don't know the format beforehand.

Contrast that with Debian build scripts which I never managed to figure out. It's dozens of layers of helpers for "common cases" with lots of Makefile magic. Completely inscrutable if you aren't already a Debian package maintainer. Very compact though.