This is one of the most ambitious homes ever seen on Grand Designs - a scaly, curving house that's reminiscent of a giant coiled snake. Stephen Tetlow is head of the Institution of Mechanical Engineers. Stephen's wife Elizabeth is a committed horticulturalist. Together they want to build a home that reflects their passions - one that pushes Stephen's engineering skills to the limit and embraces Elizabeth's deep affinity with nature. Taking inspiration from an ammonite shell found on their land in the beautiful Blackdown Hills in Devon, the house spirals onto the landscape over two levels and mixes natural materials with cutting edge technology. Construction of such a complex curving structure proves a huge challenge and progress is tortuously slow.