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.
Llanarth
Llanarth (population 1,616) is a tiny village and area in Ceredigion, Wales, situated on the A487 in between Aberystwyth and Cardigan within three miles of both Aberaeron and New Quay. Llanarth has a petrol station, post office, a primary school, a public house, a butcher, a Spar convenience store as well as a garden centre. The parish church of St David's, once devoted to St Fylltyg, is a Grade II listed building. It was refurbished in 1872. A stone in the churchyard is occasionally pointed out as birthing the Devil's footprint. According to tale, he was trying to take among the church's bells one night, yet woke the vicar, who drove him off. He left the footprint as he ran away.