Timber frame on top of a steel based which will be on ground screws. It'll be white render finished, fully insulated. Plastered on the inside and painted white. We're using a mechanical mole to route the utilities underground to save digging a trench 200ft up the garden.
Need to get WiFi down there too... not sure on the best route for that. My brother in law who's a bit of a IT whizz suggested some kind of radar system, not sure how that's works but he'll help us with that.