Just a simple small (1.5m x 1m) garden tool shed, designed and hand built from scratch. Painted in Cuprinol Garden Shades Willow, it's the first shed we've ever built and the first we've owned which doesn't leak. Yet.
First time building anything this size, largely figured it out as we went along. Planning the design in advance with the free version of SketchUp definitely helped. Framing and cladding timber was, at time of construction, £293, OSB for floor and roof and the window glass was salvaged. Add to that roofing felt, door hardware, around 800 screws, bolts, guttering, and I think total budget was around £400. Which, if you really squint, might be considered "budget".