Qurey for approval

Hi

I wish to introduce an approval for A/R Invoice  and it should  be when a certain condition meets,

The requirement is:

Based on the Warehouse and the document total i need approval for adding the A/R invoice

but when i searched this option  with standard Approval , it was not able to get done

Example :    when the end user add  A/R Invoice in which, Delhi is the Warehouse, and document total is >=3 lakhs, i need approval

any one could get me the query for this approval,,,,

Regards