I setted up shipping method with Table Rates using Price vs Destination.
Now i need for products in a specific category shipping price is calculate in the following way:
shippingprice = shippingrate*(productsnumber/2)
Example :
NormalProduct 10€
BigProduct 20€
Shipping Cost 10€
NormalProduct 10€
NormalProduct 10€
Shipping Cost 10€
BigProduct 20€
BigProduct 20€
Shipping Cost 10€
NormalProduct 10€
NormalProduct 10€
NormalProduct 10€
Shipping Cost 10€
BigProduct 20€
BigProduct 20€
BigProduct 20€
Shipping Cost 20€