Which is why this will fail. No way you can get that right. Even in a block of identical flats there will be a range of prices: what floor, proximity to lift, aspect and a hundred other little things, not to mention the condition and style of internal fixtures and fittings. Having recently seen a lot of houses, every house is unique.
I once viewed two identical flats in a new block on the same floor right next door to each other, both facing the same way. One ended up selling for 30k more than the other. Why? because the view across town was partially blocked for one of the flats by a building across the street.