First, the swap: two times memory is good. If you have a lot of memory (4 GB or
more), just over one time memory is fine.

Second, Root: for most people 20 GB is more than enough. If you really like
playing with new software, you might want more. If you are setting up a simple,
stable system 6 GB is more than enough. You want "more than you need" because
it's a disaster if it runs out.

Home gets the rest. I have a lot of videos, so I have a large hard drive. If
you just do email and a bit of word processing, a few GB is enough. (I can back
up all my non-media files on one DVD, and I have files from 15 years ago.)