Which astools repo are you using.
We generally use
https://github.com/sba1/adtools.
Unless you are trying to make a native distribution (for distribution of the native ppc compiler and tools for others) there is no need for it to be specifically /usr/local/amigaos. For that, actually it goes into /gcc with that folder have non root permissions.
Tldr: use that link. Run gild to get binutils, and gcc. You can specify your output directory by setting your CROSS_PREFIX environment variable.
It's pretty much all in the git hub main page.
If you want to checkout and build the coreutils, then checkout version 5, not 8.