gnus-home-directory

gnus-home-directory is a variable defined in `gnus.el'.
Its value is

"~/"

Documentation:
Directory variable that specifies the "home" directory.
All other Gnus file and directory variables are initialized from this variable.

Note that Gnus is mostly loaded when the `.gnus.el' file is read.
This means that other directory variables that are initialized
from this variable won't be set properly if you set this variable
in `.gnus.el'. Set this variable in `.emacs' instead.

You can customize this variable.