In case of building material rise during the contract period contractor will:

It's in the risk assessments field, depend on the contract and how much but generally I would say that there is a valid claim by the contractor.

1 / will send request to owner for addional cost 

In the agreement, there is a scope of rate variation of different items of contract . When we prepare agreement we should provide a clause from contractor end about rate adjustment during inflation. So we can go through this clause during cost of materials rises.