I am trying to post a buy it now, multiple quantity. The shipping cost will change depending on the quantity of items bought, how to show?

[popcyclepete]

I want to sell many item that are the same. Single item price for one.

When I am entering the shipping cost, I am expected to enter size and weight of package. This will depend on how many items are bought.

Not sure how to record that it will vary.

Please help.