Even for the largest businesses and the most professional contractors, things can still go wrong, take a look at these:

New Wembley Stadium
40 foot crack through three floors following an overnight storm

Scottish Parliament building
7500 defects identified. A 12 foot beam fell down during a parliamentary session

Charles De Gaulle Airport
Terminal 2E collapsed - 5 people killed in 2004

Wimbledon Media Centre
£4.6 million writ over defects

Clissold Leisure Centre
Costs of £34 milion. 59 defects occurred in the first 18 months of the building being open

South London
In 2007 black mould growing in three year old luxury apartments. Over £12 million then and expected to rise.