One thing to keep in mind: Italy, like California, is prone to earthquakes and so you need need to make sure that any cost figures you get are for a building engineered to be earthquake safe. There are some radical new ideas about earthquake-resistant design and ways to design buildings that would cost less but be as safe in quakes as ever. We are presently having a debate over that with regard to our building codes in San Francisco right now. But my point is you could get radically different cost figures depending on whether you choose to go with newer (but pretty much theoretical) designs or with the tried and true. In other words, there could be a very wide range of figures.
Beyond that, you say you have looked at the cost of buildings here such as the Millenium Tower going up in SF now. At 60 stories, it's costing $400 million. That's for residential construction. And it's got traditional earthquake resistant engineering. By contrast, One Rincon Hill is a newer and controversial design for a building of similar height and use (also residential) but it's costing "only" $290 million (for a discussion of the design, see
http://www.sfgate.com/cgi-bin/articl...AGD5JO3A41.DTL ).