how can i use paypal as payment option in my web

My Code here only accepts one item in PayPal. I want to accept many item in one transaction. And i will use loop for that ? Because i have a item in a previous page wherein the user select rooms and he can select as many as he can. The problem is, i can only accept one room ?

<form action="<?php echo $payment_url; ?>" method="post" name="frmPayPal1">
<input type="hidden" name="cancel_return" value="Cancelled.php">
<input type="hidden" name="return" value="Processed.php">
<input type="hidden" name="business" value="<?php echo $merchant_email; ?>">
<input type="hidden" name="cmd" value="_xclick">
<input type="hidden" name="item_name" value="AtticRoom">
<input type="hidden" name="item_number" value="1">
<input type="hidden" name="credits" value="510">
<input type='hidden' name='rm' value='2'>
<input type="hidden" name="userid" value="1">
<input type="hidden" name="amount" value="20">
<input type="hidden" name="cpp_header_image" value="">
<input type="hidden" name="no_shipping" value="1">
<input type="hidden" name="currency_code" value="USD">
<input type="hidden" name="handling" value="0">
<input type="image" src="http://ift.tt/IVM68V" border="0" name="submit" alt="PayPal - The safer, easier way to pay online!">
<img alt="" border="0" src="http://ift.tt/rpOo6s" width="1" height="1">
</form>

My order summary is only one. Can i add more ? But with just one clicked of the button ?