Grand Designs - The Streets continues tonight at 9pm on Channel 4.

Watch, record or stream it with a Humax set-top box.

The innovation and architectural daring shown at the UK's largest mass self-build site at Graven Hill has captured the imagination of councils countrywide. Across the British Isles, bold self-builders have been given a once-in-a-lifetime chance to build their wildest imaginings. In this third series, Kevin McCloud follows the development of some of these pioneering new projects, and revisits previous ambitious self-builds in Graven Hill and Glasgow with co-presenter Natasha Huq. Each case captures the spirit of community that these streets engender, and the determination, resilience and ambition of the builders. Shop owner and jewellery maker Karen is building her version of a mountain hut in central Glasgow, inspired by her hikes in the Scottish Highlands. After a five-year wait to get started, the project finally leaps into action when Karen and her two neighbours agree to collaborate and lay out all of their foundations together using the same contractor.

But building an architecturally ambitious house in close proximity to neighbours comes with its own set of challenges... Next door is retiree William, who, in an architecturally progressive street, is building something deliberately old-style: a home cloaked in textured grey render called roughcast. His initial plan is to get the professionals in to build the house, but his love of DIY gets the better of him, and bit by bit he takes on more and more of the work himself.