>I'm not sure what device that would be, since there are 20 gig left on my hdd.

If you use  yaourt -S foo   on an aur package this will use /tmp as directory
where the package is build.  Maybe your tmp is not big enough.

When you download the zip from the aur page, extract it and run "makepkg" in its
dir, (and pacman/yaourt -U ./freedroidRPG-svn... afterwards) this should work.