The Magnum Opus offers six different production options depending on which production time the player chooses. The amount of resources produced depends on the age of the player's town when the building was earned.
The Magnum Opus cannot be motivated, and hence, can be plundered at any time when production is finished. The production of supplies is affected by the town's happiness and by boosts of certain Great Buildings.
The building also has a secondary effect, i.e. the player will be able to spot Van Gogh himself wandering around the city!