Classic asp shipping module

I require someone to debug/complete my attempt at writing this or just rework it from scratch. The ecommerce site is working fine with a value based shipping module but we need to add something new: An additional charge for any items that are extra large or heavy. So we have a range of charges for particular brands in a new db table and for any product the admin can check a box to add the applicable charge If a customer adds one of these items to cart, the additional charge is applied in the checkout But, if a customer adds 2 of these items, or another large item from the same brand/manufacturer, there must be only one charge made. If a large item is added from a different manufacturer, then another charge will be added my solution so far is not very elegant, and is incomplete as it adds more than one charge to the cart I can provide a full copy of the site and access database for development thanks