Before you sign for the preliminary contract(the one with the agent), check the property valuation with different back first. This would give you an indication how much you can borrow from the back. Otherwise, you might have a big surprise and have to come up with the different of what you can't borrow. If the different is not much then you can always counter bargain with the bank and borrow a bit more. The bank only cares about the ability of your returning the money.