Modify the node title with the node ID before saving it
Never tried entity_buildres but you could probably use the old and tried way of adding a submit handler 

function MODULENAME_form_alter(&amp;$form, &amp;$form_state, $form_id) { 
  // this is the create form id, edit form would be node_article_edit_form
  if($form_id == 'node_article_form') {
    $form['actions']['submit']['#submit'][] = 'MODULENAME_change_title';
  }   
}

function MODULENAME_change_title($form, $form_state) {
  $node = $form_state-&gt;getFormObject()-&gt;getEntity();
  $node-&gt;setTitle('Custom Title - ' . $node-&gt;id());
  $node-&gt;save();
}