Is this more what you are looking for? I made a single frame for all the buttons, then when buttons are created within that frame, pack them as anchored to the west. The default packing will cause them to be put one on top of another (vertically). Update: don't need -side, just -anchor=>'w' for each button's pack

use Tk;
use strict;
use warnings;

# Main Window
my $mw = new MainWindow;

#GUI Building Area
my @style_sizes_array = qw(XXS XS S M L XL XXL XXXL);

my $buttonFrame = $mw->Frame()->pack();

    #checkbutton sizes setup
    for (my $ctr = 0; $ctr < @style_sizes_array; $ctr++){
        my $size_type = $style_sizes_array[$ctr];

        $buttonFrame ->Checkbutton(-text => $size_type, -padx=>20, 
                          -variable => \$ctr)->pack(-anchor=>'w');
    }

MainLoop();
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