Any shed. All depends upon what you want to do with the shed at other times. You could go cheap, or as far as a log cabin. Insulating them can help with keeping damp out - I insulated a 'cheap' summer house with the bubble wrapped foil sheets, then ply lined the lot. It stops anything, like soft furnishings going damp inside, and increases the security a bit. You'll want good security if keeping a bike in there and a TV screen for example.