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.

Its important to show clearly for this conditional in contract articls and defined both owner and contracor responsibilties in this case ..