SAP SD Contract Requirement!

Hi,

I am trying to configure a contract scenario where the company can maintain a contract value against service material. Company will generate manual sales orders and generate billing accordingly on a monthly basis as per the contract duration. I need the following to work:

Material Monthly Price x Quantity x No. of Contract Months = Total Value of Contract

Below are the things I have used so far but not able to fully execute it as per the requirement:

Contract Type : Value Contract (WK1)
Material Type : LEIS (Service w/o Delivery)
Item Category : WKN
Monthly Material Price : Maintained in VK11

I would appreciate if anybody can help.

Regards,

Qasim Sajjad