Thanks for bringing this up. I'd messed up the instructions for that bit and placed the sudo command in the wrong place.Updated it now. For anyone stuck this is the updated instructions work:

  pi@raspberrypi ~ $ git clone https://github.com/njh/perl-net-sdp.git perl-net-sdp
  pi@raspberrypi ~ $ cd perl-net-sdp
  pi@raspberrypi ~/perl-net-sdp $ perl Build.PL
  pi@raspberrypi ~/perl-net-sdp $ sudo ./Build
  pi@raspberrypi ~/perl-net-sdp $ sudo ./Build test
  pi@raspberrypi ~/perl-net-sdp $ sudo ./Build install
  pi@raspberrypi ~/perl-net-sdp $ cd ..