my $folder;

# in real code this is triggered by a button press
$folder = $mw->chooseDirectory(	-initialdir => '~', -title => 'Choose a folder',);


# triggered after user made its folder choice
# almost certainly won't work if user enters a multi-level folder structure
if (!-d "$folder") {
    print "\nCreating $folder";
    mkdir "$folder" or abort("Can't create folder $folder: $! at line " . __LINE__);  # abort sub is my own code, use die if needed
}