To configure your shipping costs, first log into your Paypal account.
Once you are logged, click on the "profile" link, found in the top navigation bar on the Paypal website.
Under the "selling preferences" column, you will find a link labled "shipping calculations". In this section, you can specify whether you want your shipping costs to be based on a percentage of the total purchase price, or a flat fee, based on a range of the purchase amount.
You should also check the box that allows transaction-based shipping values to override the profile shipping settings.
When setting up your sales items, ensure that you have selected the correct shipping method under the "require shipping address" option. If your product is shippable, choose "require shipping".