As well as four garages, the two-level home has spaces galore, including flowing semi-open plan living areas, four bathrooms, four bedrooms, a guest area/bar room, a gym, a media room and an art studio.
Its many features include cathedral ceilings and concealed ceiling lighting, deep cedar soffits, broad decks extending outside from almost every room, oversized Whitney windows and elegant, built-in bird's eye maple cabinetry.
Each of the property's five owners has put their own mark on the Glen Atkinson Rd house, but the Mills' renovations to modernise their 700sq m home under Hislop's guidance have been the most extensive.
What began as a plan to put in a new spa when the Mills missed the one at their previous house turned into a major redevelopment of the swimming pool area in 2003. This included building a free-standing gym that could double as a pool cabana, then resurfacing the large rectangular pool and repaving its surrounds with Italian sandstone.
They also created two outdoor seating areas - one with a Louvretec roof that can be opened and closed depending on the weather.
Semi-subtropical gardens that border the east, north and west sides of the house have also been upgraded with lush groupings of plants that include ligularias, aloes, ferns and palms that replaced difficult areas of lawn.
The garden revamp - overseen by Humphreys Landscaping - included transplanting three mature nikau palms by crane to the front of the 1750sq m property that spans two sites and has expansive harbour views.
The Mills have also converted an open barbecue area on the bottom level of the house into a bar room that doubles as guest quarters, with its own bathroom and a pull-down king-size bed which folds neatly back into wall cabinetry.
Except for the bar and adjoining media room, all of the main living spaces, including the large kitchen and much-used family dining area, formal dining room, formal living room and library, are on the top level.
Two sets of stairs lead to the bottom level - one from the welcoming, sunny library on the northeast side of the house and the other from the entrance foyer.
This clever configuration means guests or teenagers have their own access to the bottom level of the house.
From two garages at the front of the house, the driveway curves down behind the house to two more garages and Lesley's art studio, which looks out on to a vegetable garden and small glasshouse.
Now that their children are older and Mills entertain less often, they are ready to downsize.
The problem will be how to accommodate all of the treasures and artworks they have filled their house with over the years.