diagram help - maybe i'm thinking too hard

[desotoman]

ok, here is the sentence:

The writer saw pigeons that would not leave a building until it was actually on fire.

i have all of the sentence already diagramed, but cannot figure out what to do with "a building". i was thinking that "building" could have been the direct object of the relevant phrase "that would not leave a building", but that would make it seem like the building was a posession that was left behind by the pigeon rather than a location. i also thought that there could be an excluded "[from] a building" but that seems unnecessary. what do you think? thanks for any help.

[Tdol]

It's the object of 'leave' for me:
Leave what? Leave a building.