We got a kit shed last year - plastic sides and roof that fit into grooved aluminium uprights and supports. Cheap, waterproof and, so far, no red mite. Downsides - it's so light we had to put breeze blocks inside to anchor it in high winds, even though it was in a very sheltered spot, and we call it the "jelly shed" because it wobbles about a bit, even with the breeze blocks.