Math::Pari requires the library PARI. It even has a utility class Math::PariBuild to help during installation. Running the makefile gives the following:

$ perl Makefile.PL
Did not find GP/PARI build directory around.

Do you want to me to fetch GP/PARI automatically?

  (If you do not, you will need to fetch it manually, 
   and/or direct me to the directory with GP/PARI source
   via the command-line option paridir=/dir)
[download]

Read the sources and be inspired.