An indication of your budget would help.
If you have the means to transport it, you can often pick up used sectional concrete garages on eBay. They usually need a replacement roof but are quick and easy to reassemble and are essentially modular so can go together in any shape. They will sit on the slab so don't need any real foundations. They can be insulated and lined internally for comfort and clad externally with timber or cement cladding like Marley Cedral at a later stage when you have more money available.
For that size, if you could get a couple of garages cheap you could produce something reasonable for as little as £2,000 - about £1000 for the slab with the remainder going on roofing materials (flat EPDM probably the easiest/cheapest DIY option), used windows/door and a bit of insulation, if you can find a source of used pallets they can be used to line it internally, build racking etc.
A nicely built brick building with a tiled pitched roof, new windows and doors will be 5-10k.
