I'm looking at buying an inner city terrace and one that's on the market at the moment has been fully renovated including having had an internal wall knocked out, an upstairs bathroom added and a 9.5 m2 second living area. I'm trying to value the property based on two comparable sales that have not had these items done (but were otherwise renovated to a similar finish) - both sold for pretty much the same price. Very roughly, how much would you expect these would cost, so that I can work back from there to arrive at a value for the house?