Use the -r file operator to see whether you have read permission to the directory.

if (-r $dir) {
   find(sub { $total += -s }, $dir);
   $total = ($total / 1024) / 1024;
   $total = sprintf("%0.2f", $total);
   print OUT "$dir, $total, mb, \n";
} else {
   # however you want to deal with this condition
}
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