article: Not just any old building, mind you, but one with a gleaming metallic facade and sharp angles, the first residential property in Europe by architect Daniel Libeskind. "We haven't set a price yet," says silver-haired softly spoken developer Nikolaus Ziegert. Sapphire is still a construction site - but on a whistle-stop tour, it's easy to see its appeal to foreign wealthy buyers. In many ways, this $43m (Â£29m) development symbolises the gentrification of the city. It's certainly set tongues wagging, dividing opinion in the historical district of Mitte. The luxury property market is red hot in this neighbourhood. Almost everywhere you look from the roof of Sapphire, there are cranes at work, constructing a new Berlin. Just over a decade ago, Berlin's mayor declared the city "poor but sexy", a reputation that helped attract innovative and creative businesses. But now, with its fortunes rapidly changing and the gentrification this brings, is Berlin in danger of becoming a victim of its own success? Its population has been growing fast, and in the past five years so have rents, pricing some local residents out. For Mr Ziegert, business is booming. He set up his property company 30 years ago in West Berlin, when the city was still divided, with just three employees. Now, he has a turnover of some $300m, and 180 staff. Mr Ziegert enjoys being chauffer driven in a vintage Maserati. But he doesn't fit the stereotype of a brash property developer. He is aware of the tensions development can create. "Gentrification has to be seen from two angles," he says. "Of course, the first is that of the tenant. "In Berlin, when the prices rise, people feel insecure. "On the other hand, gentrification also means change and progress. "And even if it's unpleasant for some, it remains very important for the city that investment comes in." In many ways, Berlin is still a city of two halves. On the one hand, there is an incredibly fast-growing community of hi-tech start-ups. On the other, the city's unemployment rate is more than 10%, compared with just 6% for the rest of Germany. Michael Plaumann lives in a homeless shelter in Neukoelln, an area earmarked by developers as the next property hotspot. To supplement his unemployment benefit, he sells a homeless newspaper on the trains of Berlin. "It's very difficult for me to find my own apartment for myself," he says. "That's why I've been living in a shelter for a while already, because the apartments have become very expensive, and for as someone who receives benefits, it is just too expensive." The $900 (Â£600) cost of his shelter accommodation is covered by his benefits. Should he find an apartment of this own, he'd be unable to claim the full rent because of a cap, which could price him out of his neighbourhood. "I want to live in my neighbourhood. That's Neukoelln. I've been there for 15 years," he says. "What bothers me is that in Berlin, more and more neighbourhoods are becoming ghettos. Berlin is not changing for the better." Lisa Jaspers earns
summary: How many millions would you pay for a penthouse apartment in a futuristic new development with a panoramic view of Berlin?