Gentoo is mostly just BLFS and ALFS from there, with more available packages, and centralized 'USE FLAGS' ( https://wiki.gentoo.org/wiki/USE_flag ) which could be considered one of Gentoos USPs.
Funny you should mention it, that was the first I tried, and I never tried again. Only until just recently had I even had the thought. Needless to say I was not successful my first try.
Gentoo is mostly just BLFS and ALFS from there, with more available packages, and centralized 'USE FLAGS' ( https://wiki.gentoo.org/wiki/USE_flag ) which could be considered one of Gentoos USPs.