S4·E3 Revisited - Buckinghamshire: The Inverted-Roof House

In November 2001, Tom and Judy demolished a bungalow and started building an infinitely more ambitious house. Designed on different levels, with glass walls and exposed steelwork, it was to be a miraculous piece of engineering, giving the couple and their two young children a beautiful, technologically advanced home. Tom appointed himself project manager—a job that proved to be more challenging than he had expected. Grand Designs 3 followed the first 16 months of the build. As Grand Designs 4 goes on air, how close is it to completion?