#!/usr/bin/perl
use strict;
use warnings;
use Data::Dumper;

my @arr = qw(aa bb cc dd ee ff);

sub build {
    my %hash;
    my $ref = \%hash;
    while (defined (my $element = shift @_)) {
        $ref = ($ref->{$element} = @_ ? {} : 0);
    }
    \%hash;
}
print Dumper build(@arr);