Mine

print "id,type,level\n";
for (my $x = 1; $x <= $#sortedbuildings; $x++) {
   if (exists $sortedbuildings[$x])
   {
     print "$x"; 
     for (my $y = 0; $y <= $#{$sortedbuildings[$x]}; $y++) {
       print ",$sortedbuildings[$x][$y]"; 
       } 
     print "\n";
   }