New Condition type for SAD- Special additional Duty

Hi gurus,

I have been told to configure a new condution type for SAP-Special Additional Duty, which is charged on BEDCESSSHCESS, CST VAT will be charged in SAD also. This should be applicable for sale of imported materials. but where as in normal sales SAD should not be charged.

So please tell me do i need to create a new condition type, if so how shall i do the offset..

can anybody tell the flow..