Question: Which building that was in position of Earls of Selkirk until the early 1900s was built by Sir Thomas Maclellan?

Context paragraphs:
Mast Farm: The Mast Farm is a historic farm located near Valle Crucis, Watauga County, North Carolina and is now an Inn.  In the late 1700s, Joseph Mast walked from Pennsylvania and settled on much of the land that is now Valle Crucis.  Around 1810, his son David built the two-room log cabin which now sits facing the main house at the Mast Farm.  David’s son Andrew began building the main house around 1880.  Andrew’s son, D. Finley Mast, completed it in 1896.  A photo of the house in the early 1900s shows a sign stating simply, “BROOKSHIDE FARM, D. FINLEY MAST, ONE HALF MILE TO POST OFFICE.”  Originally, the main house consisted of only the part closest to the road – three stories high, with two rooms on each floor.  Like most large homes with open flames for cooking, it had a detached kitchen.  The main house is a two-story frame dwelling with a gable roof.  In the early 1900s, Finley and his wife, Josephine, began to make additions to the house and to operate it as an inn.  Over a period of about twenty-five years, five different symmetrical additions were completed, ultimately comprising thirteen bedrooms – and one bathroom.  Other contributing buildings are an eight-sided gazebo (1890), wash house, spring house, meat house, log woodhouse, apple house (1905), weaving house (c. 1812), blacksmith shop, and gambrel roofed barn.  The weaving house served as the original farm house.

Lord Mayor of Liverpool: The office of Lord Mayor of Liverpool has existed in one form or another since the foundation of Liverpool as a borough by the Royal Charter of King John in 1207, simply being referred to as the Mayor of Liverpool.  The current Lord Mayor of Liverpool is the Right Worshipful Councillor Malcolm Kennedy who has held the post since May 2017.  The most prominent Mayors were the Stanleys of Knowsley, of which Sir Thomas Stanley (son of the 3rd Earl) and the 4th, 5th, 6th, 7th, 8th, 9th, 10th, 16th and 18th Earls of Derby have held this office since ancient times.  The Molyneuxs of Sefton have also held this office on numerous occasions over the centuries: Sir Richard Molyneux, his grandson Sir Richard Molyneux Baronet, the 1st Viscount Molyneux and the 7th Earl of Sefton.

Bloomington Central Business District: The Bloomington Central Business District is a historic district in downtown Bloomington, Illinois.  The district includes roughly twelve square blocks of the city and encompasses 140 buildings, 118 of which are contributing buildings to the district's historic character.  The 1901 McLean County Courthouse, the center of government of McLean County, is the focal point of the district.  The other buildings in the district were built between 1842 and 1942 and are primarily commercial.  The Miller-Davis Law Buildings, two of the oldest buildings in the district, were built in 1843 and represent the early period of Bloomington's development.  Bloomington's commercial core grew rapidly during the 1850s and 1860s after two railroads opened in the city; while the 1854 Gridley Bank is the only surviving pre-1857 building from this period, several more remain from the later part of the boom.  The city continued to grow, and its business district continued to expand, from 1860 until 1900; however, a fire destroyed much of its downtown in 1900.  Several buildings in the district date from the rebuilding period of the early 1900s.

MacLellan's Castle: MacLellan's Castle in the town of Kirkcudbright, southwest Scotland, was built in the late 16th century.  It stands in the centre of Kirkcudbright, on the south side of the River Dee which flows into the Solway Firth.  The L-plan castle was the residence of the MacLellan family from whom it derived its name.  The family sold the castle in 1752, and from 1782 to 1912 it was held by the Earls of Selkirk.  Today, the site is curated by Historic Scotland.

Baron Stanhope: Baron Stanhope, of Harrington in the County of Northampton, was a title in the Peerage of England.  It was created on 2 May 1605 for Sir John Stanhope, Vice-Chamberlain of the Household between 1602 and 1616.  He was the son of Sir Michael Stanhope and the brother of Sir Thomas Stanhope, ancestor of the Earls of Chesterfield, the Earls of Harrington and the Earls Stanhope.  Lord Stanhope was succeeded by his son, Charles, the second Baron.  The title became extinct on his death in 1675.

Thomas Maclellan of Bombie: Sir Thomas Maclellan (died 1597) was Provost of Kirkcudbright and father of Robert Maclellan, 1st Lord Kirkcudbright.  He was responsible for the construction of MacLellan's Castle in the town.

Oliver Gascoigne: The Oliver Gascoigne family originated at the point that Richard Oliver, originally of Castle Oliver, Limerick, Ireland, inherited the fortune of Sir Thomas Gascoigne of Parlington Hall, Yorkshire, in 1810.  Sir Thomas made it a stipulation of his will that Richard add 'Gascoigne' to his name.  Richard had married Sir Thomas's stepdaughter, Mary Turner, in 1804.  Richard and Mary had two daughters, Isabella and Elizabeth, who inherited their parents' fortune in 1843.  The sisters demolished their ancestral home in Ireland, and built a new Castle Oliver a few hundred yards to the north east.  The castle still exists.

Everett Building (Huntsville, Alabama): The Everett Building is a historic commercial building in Huntsville, Alabama.  Built in 1899, it represents the Commercial Brick style of the late 1800s and early 1900s that eschewed the applied decoration of the Victorian style.  The two-story building is divided into five storefronts, although only the southernmost two have entrances today.  The upper floor is divided by pilasters between tightly spaced, one-over-one sash windows. Decorative patterned reliefs sit below each window.  The building is topped with a parapet that has a course of dentils between courses of stepped brick.  The center part of the parapet is raised, and flanked by a short, capped column pieces.  The northern bay is visually separated from the others by a pilaster stretching the entire height of the building, and was formerly left unpainted, suggesting it may have been built at another time.  A covered, tree-lined alley separates the building from the Yarbrough Hotel to the north.  The building was listed on the National Register of Historic Places in 1980.

Sir Thomas Boyd: Sir Thomas Boyd of Kilmarnock was a 14th-century Scottish landowner and lord of Kilmarnock in Ayrshire.  He was the son of Sir Robert Boyd, who fought at the Battle of Bannockburn.  In 1346, he was taken prisoner at the battle of Neville's Cross.  He is known for building the earliest parts of Dean Castle in around 1350, and the castle still stands today and is open to the public.  Sir Thomas was succeeded by his son, Thomas (died 1432).  Sir Thomas' later descendants were the Earls of Kilmarnock.

Dewar Cup: The Sir Thomas Dewar Cup, more commonly known as the Dewar Cup, was the trophy awarded to the winner of the National Challenge Cup/Lamar Hunt U.S. Open Cup competition.  It is named after Sir Thomas Dewar as a tribute to his works promoting soccer in the U.S. in the early 1900s.  Though the trophy is now on permanent display at the National Soccer Hall of Fame in Oneonta, New York, each winning club's name is still added to the base of the trophy each year.

Supporting paragraphs: Thomas Maclellan of Bombie MacLellan's Castle
Answer: MacLellan's Castle