use File::Find;

my $dir = 'c:/test';
my $size = 0;

find( \&size, $dir );

sub size {
   # we get each filename in $_
   my $file_size = -s $_;
   $size += $file_size;
   print "Found $_ $file_size Bytes\n";
}

print "$size Bytes in '$dir' and all subdirs\n";