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.
Selkirk
Selkirk is a town and also historical royal burgh in the Scottish Borders Council area of southeastern Scotland. It lies on the Ettrick Water, a tributary of the River Tweed. The people of the town are known as Souters, which implies cobblers (shoe makers as well as menders). At the time of the 2011 census, Selkirk's population was 5,784. Selkirk was previously the county town of Selkirkshire. Selkirk is one of the oldest Royal Burghs in Scotland and also is the site of the earliest negotiations in what is currently the Scottish Borders. The town's name means "church by the hall" from the Old English sele ("hall" or "mansion") and also cirice ("church").