Milestone Contract Creation in SAP SRM

Hi gurus ,

I am trying to create a Milestone based contract in SAP SRM but am unable to do it.

I could find options for volume discount , header level discount based contracts but not milestone ones.

I want to setup a contract where I will be paying a supplier part of the value of the contract every month (e.g.10%)

Any help would be appreciated.

Thanks ,

Paramesh