It depends on the material you use, but if your flat roof is installed correctly it should last for at least 10 years, and at least 20 if a material other than felt is used. Always question a roofing company when they quote to find out what materials they use and what guarantee's they offer.
South Brent
South Brent (population 2,822) is a big village on the southern side of Dartmoor, England, in the valley of the River Avon. The parish includes the tiny communities of Aish, Harbourneford, Lutton, Brent Mill, as well as many scattered farmhouses. It is five miles (8 kilometres) north-east of Ivybridge as well as 14 miles (22 kilometres) east-northeast of Plymouth. On the high moorlands are numerous hut circles, units, and barrows, all dating from the Bronze Age. The manor of Brent came from Buckfast Abbey from the moment of the foundation of the abbey in the early 11th century. It was bought at the Dissolution by Sir William Petre, a huge receiver of monastic spoils in South Devon. South Brent was initially a woollen and also market centre with 2 annual fairs. Brent Hill is the steep hill just outside the village from which it takes its name (Old English brant-- steep). On it are the ruins of an ancient structure, intended to have been a church, and of a windmill built concerning 1790.