Magento Maximum Allowed Order QTY

ake a look @ Magento Maximum Allowed Order Amount, you would have to create a custom module to add this feature.
Create an observer for sales_quote_save_before

<config>
    <frontend>
        <events>
            <sales_quote_save_before>
                <observers>
                    <mymodule_custom>
                        <class>Mymodule_Custom_Model_Observer</class>
                        <method>LimitOrderqty</method>
                    </mymodule_custom>
                </observers>
            </sales_quote_save_before>
        </events>
    </frontend>
</config>

In your observer

<?php  
class Mymodule_Custom_Model_Observer {

public function LimitOrderqty(Varien_Event_Observer $observer){ 
   $cart = Mage::getModel('checkout/cart')->getQuote();
   $customer = Mage::getSingleton('customer/session')->getCustomer();
   $allowQTY = $customer->getLastsaleqty() + (int)($customer->getLastsaleqty()*$customer->getGreaseqty()/100);
  if ($cart->getItemsQty() > $allowQTY) {
            Mage::getSingleton('checkout/session')->addError('You are not allow to add that QTY in your cart. Your Approved QTY limit '.$allowQTY);
   
   Mage::app()->getFrontController()->getResponse()->setRedirect(Mage::getUrl('checkout/cart'));
            Mage::app()->getResponse()->sendResponse();
            exit;
        }
 }
   
}