Google's Earth and Maps applications are fantastic, but they have a slight problem - they're flat. The vast majority of locations have some form of terrain data - but that data comes from satellites which can't work out individual buildings. Some cities, like San Francisco, have had their terrain modelled, but most are featureless.
Google doesn't have the manpower to model all those buildings itself, so instead it's turning to the wilds of the Internet for help. It's launched Building Maker, which allows anyone to pick a spot on the globe and start making buildings out of simple 3D shapes. Whole buildings can be put together within minutes.
At the moment, only 50 cities are accessible. Only two of those are in the UK - Cardiff and Birmingham. If you're not sure where to start, then, Google will offer you a random location in a city worldwide instead. It's all done within the browser, though you might need a few plugins to make it work.
When you've made your model, you can keep track in your Google account of what you've built, and go back and edit models at a later date. You'll be credited for any buildings that you contribute.
In our brief testing, we found it lots of fun, if a little tricky to get the exact positions of the corners right. If you find you're having trouble lining something up right, then it's often easier to delete that block and start from scratch, but experimentation will give you most of the knowledge you need relatively quickly.