Firstly, your subroutine is not going to do what you think. This line

my $tgs = @_;
[download]

is going to assign the number of elements in @_ to $tgs because the LHS is in scalar context. Do this

my ($tgs) = @_;
[download]

or this

my $tgs = shift;
[download]

instead.

Rather than trying to make the contents of $tgs part of the hash name, you might be able to accomplish what you need using a HoH structure. Something like

my %Test_hash;
...
sub xyz
{
    my ($tgs) = @_;
    $Test_hash{$tgs} = {a => 1, b => 2};
    ...
}
...
[download]

I hope this is of interest.

Cheers,

JohnGG