SQL Server - Creating a Stock Trigger

Hi I was wondering if anyone could help me, Im trying to do a trigger which will reduce the quantity of items in stock, however it isnt as easy as it sounds.

Ive designed a database for a carpentry company, they make garden furniture products for companies. When a company orders garden furniture products such as a picnic bench, tree seat etc I have to try to reduce the number of components which make up those products from the items in stock.

Therefore I think I need a trigger on my sales order line table which looks up the items that make up the product requested from the component table inorder to reduce these individual component items in my Item table which contains the stock quantity.

Any help suggestions would much be appreciated.

Sounds sensible to me. Where are you struggling?!