Mike,
Thanks for the prompt and very clear reply. I just want to check that once I copy the gist code into a new functions.php file in my child theme the Add custom field box should show a new field to be selected from the dropbox. This is not happening now (using Twenty Fourteen theme) and I am sure that it is reading the functions.php file (If I add an extra <?php at the beginning it shows an error when I try to see the page that has the tiles). If it should automatically create the field, then I am guessing I may have a problem with the theme or other plugins.
Once again, thank you for the plugin and the quick reply.
