Sir Derf
Adept
And Orcs require Tools.Shouldn’t also orcs be considered? Grounds of Orc Strategist requires nothing for its production. Training Grounds require one orc for each Orc Strategist (or less if you consider Simia wonder). Where do you get them? Doesn’t your source also require some space?
EDIT: And orcs are not the only thing. The building has some requirements just to exist/be built.