The mason James McBlain executed all the decorative carving and much of the subsequent building for the Earl. Italian stuccadores were also employed, chief among whom was Placido Columbani.
Downhill is characterised by a three storey front, facing south and with two long wings at the back of this. Originally these wings terminated in domes topped with ornamental chimney-pots. The wings were continued in ranges of outbuildings, forming inner and outer yards, and ending towards the sea in two immense curving bastions of basalt.
The main house block was faced with freestone from Dungiven quarries, about 30 miles away. The basement is rusticated and the storeys above decorated with pairs of Corinthian pilasters, topped by Vitruvian scroll course, a cornice and parapet.
Sadly the interior of the house shows little of its original character. The house was almost entirely gutted by a fire which broke out on a Sunday in May 1851. The library was completely destroyed and more than 20 pieces of sculpture had been ruined. Most of the paintings were rescued, but a Raphael, The Boar Hunt, was reported destroyed.
This was the house of which the Earl Bishop had written to one of his daughters from Rome in December, 1778, that: 'I am purchasing treasures for the Down Hill which I flatter myself will be a Tusculanium.'
Downhill House in the 20th century
In his later years, the Earl Bishop spent very little time in Ireland. His Irish estates were administered by a distant cousin, Henry Hervey Aston Bruce, who succeeded him following his death in 1803.
In 1804 Henry Hervey Aston Bruce was created a baronet and Downhill remained with the Bruce family until at least 1948, though the family rarely lived there after around 1920.
The only other occupation of the house came about during WWII when the site was requisitioned by the RAF. The house was subsequently dismantled after the war and its roof removed in 1950.