Designed by Robert England, it was built of kauri by Rennie and Pearce builders between April 1899 and September 1900. It was the largest wooden residential structure in New Zealand at that time. It was constructed for the Scottish philanthropist and immigrant, Allan McLean, when he was 78 years old and he lived in it for the remaining seven years of his life. The building was registered on 7 April 1983 as a Category 1 heritage building.
The mansion is built to a rectangular plan in Jacobean style, with three stories. The structure's concrete foundation is to a depth of 3 feet (0.91 m) over a pile foundation of 3 by 2 feet (0.91 m × 0.61 m). It has a floor area of 23,000 square feet (2,100 m2). The 53 rooms include 19 bedrooms, nine bathrooms, and six servant rooms. The wall frames are of kauri wood fixed with wall plates. The floor is made of wooden joists and sleepers. The dwangs are fixed in an angular direction to give a wavy appearance. The roof domes are made of iron sheets and the pinnacles are of cast-iron crestings, a French design feature. Corrugated iron sheets are used for the roof. The water gutter heads and pipes for draining rain water from the roof are also made of cast iron, though the pipes probably were fitted later, in 1915. The chimneys are also provided but their heights were curtailed at some later stage.
The interior fittings are elaborate and ornamental, typical of a Jacobean house. The crafting of the interior ceilings, plasters, mouldings and balustrades is the handiwork of Christchurch artisans. The ceiling depicts roses with mouldings of simple design at the wall corners. The two rooms on the ground floor near the entrance have elaborate coffered ceilings with a well-carved, gilded, central decorative. The top part of the doors in each of the main rooms has a well-ornamented wooden typanium. The balustrades of the staircase and the newel post have been featured with thistles and flowers, an emblem of Scotland (a reminder of the owner's homeland). The newel posts in particular have carvings of acanthus leaves and beading; brass lights which decorate the posts are also fitted over them.
The furnishings were of an exclusive design chosen specially by the housekeeper and a fabric expert from Paris. The wall fabrics are of satin brocade in apricot cream colour; they were also fitted under the expert's guidance. The walls of the drawing hall, next to the outer hall, were very elegantly furnished with satin fabrics featuring "buttoned braiding at the skirting boards". Numerous lights, elegantly designed, were fitted on the walls and ceilings. The white marble fitted fireplace, fixed with ornate brass, completed the scene. The staircase in the hall was fitted with a red carpet and the walls of the hall were embellished with coloured velvet fabrics. The dining room walls were covered with curtains made with satin fabrics which added to the grandeur of the dining room along with an elaborate chandelier and a fireplace fitted with black marble. The silver room was fitted with shelves, from flooring to the roof, filled with "tureens, entry dishes, epergnes, teapots and cutlery". The fittings in the bathroom were all made of brass, and the bathtubs were of porcelain.
At the entrance stood two elaborately carved hat stands. These were in the form of a 7 feet (2.1 m) mahogany tree trunk with branches embossed with a traditional design of bear and cub. The drawing room displayed a mirror bordered with polished mahogany which was fitted with bronze and marble statues. The grandfather clock was a display item in the room. The settees, high backed and in a wing shape were upholstered in a burgundy colour. The ornamental chairs were fitted with regency brocade fabrics while a Persian carpet was a striking feature of the room. A retractable table was also part of the drawing room furnishings. Paintings of Victorian, Flemish and Scottish landscapes were hung from rods in the main rooms on the ground floor and also in the gallery on the first floor. The dining room was fitted with a large table made of oak to seat 14 people, with all related fittings in the room also made in oak. The green and gold dinner service with monogram of A.L. formed part of the dining room cutlery, and the crockery consisted of large dishes to serve turkey and trout. The foyer and the inner hall had high mirrors and velvet curtains. Greenery was added to the setting of the halls and main rooms in the form of potted plants.