Yes, your shed does need a base. This is to give it a solid, level foundation. Open soil will not help with the longevity of the shed itself or the contents within. The best materials to use to make your shed base are concrete, natural stone or wood.
Leven
Leven is a seaside town in Fife, set in the east Central Lowlands of Scotland. It lies on the coastline of the Firth of Forth at the mouth of the River Leven, 8.1 miles (13.0 kilometres) north-east of the town of Kirkcaldy and also 6.4 miles (10.3 km) east of Glenrothes. According to a price quote absorbed 2008, Leven has a population of 8,850. The community creates part of the Levenmouth conurbation, which has an overall population of 37,651.