Aaron Gray writes ("Re: Debian distro build system"):
> I basically want to
>
> a) be able to build a Debain distro myself such as Jessie for testing purposes
>
> b) be able to make bespoke modifications to this
All the source code and tools are available. But sadly it's a bit
complicated. (IMO this should be easier than it is.)
Some resources
https://wiki.debian.org/DebianInstaller
https://wiki.debian.org/MassRebuilds
https://wiki.debian.org/DebianWannaBuildInfrastructureOnOneServer
https://manpages.debian.org/stretch/sbuild/sbuild.1.en.html
https://manpages.debian.org/stretch/dpkg-dev/dpkg-buildpackage.1.en.html
https://manpages.debian.org/stretch/dgit/dgit-user.7.en.html
(Full disclosure: the last link there is a plug - I'm the author)
Good luck.
Ian.
