One way to start is to dl all of the srpms and install them.. you will need a big disk. These will all install under /usr/src/. The structure you get will be something like what RedHat has, you will have source tar.gz's patches and spec files which are used to build and compile these packages into rpms. You will need to write a make file at the root of your srpms to auto build everything but thats it. Once you have this you can force your rpm installs to a particular dir structure possibly /var/myDistro. You can pick and choose your packages , you can upgrade at your own pace.
Note there is a lot more to this if you are new to linux, rpm, make, chroot, mkisofs, possibly pxe boot.