Re-Order Level - How many to Order (column to be able to manually populate)

It would be nice to have a column which is visible on the purchase order page of how many items we want to take that product up to. i.e. the maximum we want to have in stock. At the moment we use 'product special attribute' as a label for other things too so this solution isnt ideal and requires manually calculating and adding products to a purchase order. Really it'd be nice to populate a column and then it be able to automatically add these based on currently inventory and if it was below manual re-order level.