Best advice is to avoid Berlin. It is situated in the former East Germany and does not have much to recommend it as investment material (I like the city, but wouldn't invest three). The city is also 60 billion in debt, which the government refuses to pay, so property taxes look certain to be a major issue in the medium term. Prices for medicre residential property in particular are being pushed up by Irish and UK buyers waving chequebooks and making comparisons to prices back home.
If you want to invest in Germany, go to Frankfort, Munich, or any other city with a better local economy.