A relative of mine is building a house right now. They bought a property and they need to start construction within 1 year, or else they loose that property. Not sure if it works that way everywhere in Germany.
The UK has time limits on planning permission too, but they are quite long - 3 years is the default. Also the limits only apply to the commencement of the work. You can (and people do) get around this by digging a hole or laying a small part of the foundations, and then they do nothing else. So with really a very small amount of effort, you can "land bank" indefinitely. The government shows no signs of wishing to fix this, since forcing up the price of houses to absurd new highs is policy.
