The couple fought and won a battle with the local council to overturn planning regulations and rebuilt the one-bed chalet from the ground up.
Now the luxury pad boasts the latest interior fittings, including posh skylights, bespoke kitchen and a natural “spa” complete with a hot tub and heated outdoor shower.
Bi-fold doors offer breathtaking views of Whitsand Bay on the south Cornwall coast.
Searches show the couple paid £125,000 for the 300sq ft shed in 2013 and now stand to sell for seven times as much.
Mother-of-one Katherine said: “It was the size of the plot that really attracted us and the sense of isolation from the other chalets dotted along the cliff.
“It was initially our intention to live there but with the arrival of our baby, Ella-Rose, we decided to turn it into a holiday let.”
The Woolers now live in New Zealand but spent countless hours commuting to the site.
Katherine, 44, added: “We lived in Dorset during the build and were doing day round trips to Cornwall to oversee the build – with a six-month-old baby!
“To say it was stressful was an understatement – but it was worth it.”