(untested)

my %windows;

my $current_location;

while (<>) { # read from stdin
    chomp;
    if ( /^\d+\s+\d+/ ) {
        $current_location or die "bad input";
        $windows{$current_location}{$_}++;
    }
    else {
        $current_location = $_;
    }
}

for my $location ( sort keys %windows )
{
    print "\n$location\nwidth height quantity\n";
    for my $dimensions { sort keys %{ $windows{$location} } ) {
        print "$dimensions $windows{$location}{$dimensions}\n";
    }
}
[download]

But /me smells homework.