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 ..

The missing files aren't stopping you, it's the last line "mkdir _build: Permission denied".

To get around it I just ran the build as root ;)

Ah yeah, thank you!

I have everything 'working' now, although it's quite glitchy, making loads of static sounds. After a few restarts etc. it is playing okay now, I don't want stop playing it incase it doesn't work again!