How much of a mortgage can we get?

My partner and I are planning on buying a house that is worth 270000 but it is not finished. Can we get a mortgage of 300000 to finish the house? Also will the stamp duty be calculated on the value of the house or the mortgage amount?

Stamp Duty is calculated on the value of the house.

As for borrowing 300k, you will be able to if the valuer reckons its worth 300k now or your mortgage company is still operating on 06 guidelines of give 110% mortgage.

You won't be able to borrow more than the purchase price....

you can borrow which every is lower , the purchase price or the valuation....