Hume appears to have planned a comprehensive work on the birds of India around 1870 and a "forthcoming comprehensive work" finds mention in the second edition of "The Cyclopaedia of India" (1871) by his cousin Edward Balfour. His systematic plan to survey and document the birds of the Indian Subcontinent began in earnest after he started accumulating the largest collection of Asiatic birds in his personal museum and library at home in Rothney Castle on Jakko Hill, Simla. Rothney Castle, originally Rothney House was built by Colonel Octavius Edward Rothney and later belonged to P. Mitchell, C.I.E from whom Hume bought it and converted it into a palatial house with some hope that it might be bought by the Government as a Viceregal residence since the Governor-General then occupied "Peterhoff", a building too small for large parties. Hume spent over two hundred thousand pounds on the grounds and buildings. He added enormous reception rooms suitable for large dinner parties and balls, as well as a magnificent conservatory and spacious hall with walls displaying his superb collection of Indian horns. He used a large room for his bird museum. He hired a European gardener, and made the grounds and conservatory a perpetual horticultural exhibition, to which he courteously admitted all visitors. Rothney Castle could only be reached by a steep road, and was never purchased by the British Government.