Kevin McCloud meets Clinton Dall from Sussex, a self-made businessman and father of four aiming to build one of the largest homes ever featured on the show. Dall wants the end project to be perfect - from the finish of his mirrored cruciform steel columns, to how the floor tiles line up with the dining room table, and is willing to spend whatever it takes to achieve his vision. However, the construction represents a huge risk, as down one road lies abject failure and financial ruin, while down the other, is the creation of something sublime and almost heroic.

Boat enthusiast James Strangeways invites Kevin McCloud to survey progress on the construction of his new home, which his architect nephew Ben Hebblethwaite has designed to be as 'un-houselike' as possible. James has spent the past 35 years travelling the canals and waterways of Britain, and despite never liking houses, has decided now is the time to put down roots on dry land. Ben hoped a home standing on stilts above a marsh, and incorporating ship-like qualities such as a keel-shaped roof, will be enough to satisfy his boat-mad uncle. However, Ben's contractor goes into liquidation a few months into the project, taking £87,000 of the £300,000 budget, and when James decides to make a few tweaks to the design, alarm-bells begin to ring for the young architect.

After recovering from a life-threatening brain haemorrhage, Bram Vis, his wife Lisa and their two children want to build a house for sharing on a seaside plot on the Isle of Wight. Kevin McCloud follows the family's progress as they build an ambitious home complete with entertaining spaces and a swimming pool. However, the sheer scale of their project soon becomes clear when their original £850k budget spirals out of control.

Kevin McCloud follows the progress of 37-year-old Angelo Mastropietro, as he transforms a damp, dark and abandoned cave in Worcestershire. Having recently been diagnosed with multiple sclerosis, Angelo wants to create a retreat to help him cope with the news and become a 21st century caveman. He has a budget of £100,000 and plans to almost single-handedly carve, cut and drill into the hillside to make the cave comfortable for contemporary living. However, there is no manual for a project of this kind, and the unique challenge soon becomes an obsession.

Kevin McCloud follows the progress of teacher Michele Long and architect Michael Howe, who want to restore and transform a 100-year-old blacksmiths in County Antrim near the coast of Northern Ireland. With virtually no practical experience, Michael wants to do as much of the project as possible by himself. However, the weather on the coastline is fierce, and the freezing weather coupled with a tight budget of 150k means the build is stretched from one to three years.

Kevin McCloud follows the progress of private chef Ed Versluys and pilates instructor Vicky Anderson, who want to convert a concrete cowshed in the Somerset countryside into a three bedroom home. With the help of one young builder and the knowledge they can learn from the internet, the couple plan to project manage the conversion themselves. However, they have only eight months and a budget of just over £200k to make a warm and comfortable home with straw bale walls and wide expanses of glass.

Kevin McCloud follows the progress of Stephen Yeoman and Anita Findlay, who want to build a cutting-edge, post-industrial house covered in rusty metal. However, their prominent riverside plot in the traditional and architecturally conservative area of South Downs means everyone will be watching. The project proves to be a real rollercoaster when the fitting of the rusty steel cladding goes wrong, cash flow problems threaten to bring work to a halt, and the couple announce that a baby is on the way.

Kevin McCloud revisits Andy and Nicky Bruce who were building an experimental amphibious house on a small island on the Thames in Buckinghamshire. They spent £1.2 million on one of the most ambitious Grand Designs ever, but the logistical headache of building on an island only accessible by a narrow footbridge soon became clear. Heavy machinery was swept away by the river, contractors were changed, and the site was hit by severe storms, causing delays and resulting in an unfinished and untested building. Kevin returns to find out what living on a regularly flooded piece of land is like, and whether the floating home performed when the river burst its banks in January 2015.

Kevin McCloud returns to north Cornwall to see one of his favourite Grand Designs, and discover whether Rebecca Sturrock and Gregory Kewish have been successful with their ambitious plans. Their project, to reinforce the walls of an old bungalow and put a new living space on top made entirely of cross-laminated timber, soon ran into difficulties, but now fully complete both inside and out, Kevin finds out whether this innovative house is really big enough to accommodate a growing family.