As an architect, Desprez designed in a monumental, neoclassical style influenced by his study of Greek and Roman ruins in the south of Italy and in Sicily. A good example of this is Hämeenlinna Church in Finland - Finland at that time still being part of the Swedish kingdom - completed in 1799. His greatest project was one never realized: the magnificent new palace planned by the King for the Haga Park outside Stockholm. Because of lack of money, only the foundations were ever built and the project was abandoned after the assassination of the King. The smaller "royal pavilion" which stands at Haga was built by another architect, Olof Tempelman. His most significant completed project was the conservatory building in the new botanical garden in Uppsala, inaugurated after his death on May 13, 1807, the 100th anniversary of Linnaeus's birth. He also built the Villa Frescati in 1791-92 for Gustaf Mauritz Armfelt, after which the whole Frescati area in Stockholm later was named.