A cache of his drawings was discovered, curated and exhibited in 1989 by Ian Gow at the Royal Commission on the Ancient and Historical Monuments of Scotland, entitled "John Douglas – William Adam's Rival?".
A broader study of his work shows how his designs explored the plastic treatment of the volume and the materiality of elevation in rather eclectic manners beyond his period, often though deemed too fashionable or personal.
[13][14] He is an interesting less-known case of the early 18th century context in Scotland characterised by the professional establishment of architectural practice and a more conscious exploration of personal styles and external influences, often treatises.
Analysis of his major buildings (Archerfield (1745-9), Finlaystone House (1746-7), Wardhouse (1757); student halls in St. Salvator’s (1754–58); the disastrous intervention in Holyrood Abbey church (1760); and the town halls for Lochmaben (1756) and Campbeltown (1760)) show a characteristic treatment of the materiality of elevations and a mannerism that is restrained and more influenced by the earlier Palladianism of Inigo Jones than James Gibbs.
More on his professional practice can be revealed from the study of the building contracts for Archerfield and Finlaystone for example, as also the litigation with his journeyman George Paterson,[15] which also confirm disputed authorship of his work A book by Howard Colvin lists several of his projects, but some of the facts are incorrect (for example, Douglas was indeed responsible for the disastrous repair of the church of Holyrood Abbey in 1760 and the dispute over non-payment of the rest of his fees was resolved only after his death).