How to build a build environment for all of Ubuntu?

[Dan Kegel]

Where is the procedure to build all of Ubuntu
from sources documented?
Ideally I'd like to have a really clean bootstrap,
i.e. be able to cross-build the core build environment
which is then used to build the rest of Ubuntu.
Thanks,
Dan

p.s. I'm one of those odd birds who actually likes cross-compiling.
A while ago, I wrote a script to make it easier to build gcc/glibc
crosscompilers;
see http://kegel.com/crosstool