Mage. Set custom layout by customer group.

mage_set_custom_layout_by_customer_group.md

  protected $_customer_groups = array('NOT_LOGGED_IN', 'Genaral', 'Wholesale', 'Retail');

    /**
     * Get current customer group and update handle depend from current group
     * Observe event "controller_action_layout_load_before"
     * 
     * @param Varien_Event_Observer $observer
     */
    public function setTemplate(Varien_Event_Observer $observer) 
    {
        $group_id = Mage::getSingleton('customer/session')->getCustomerGroupId();

        $observer->getEvent()->getLayout()->getUpdate()
           ->addHandle('CUSTOMER_GROUP_' . $this->_customer_groups[(int)$group_id]);
    }