On the opposite side of organized nests, I vote for Mourning Doves for the most haphazard, half-*ssed nestmakers. They're notorious for disheveled nests which barely stay together, in odd places:
https://www.wild-bird-watching.com/images/dove-nest-on-hangi...
We had a pair in a planter box whose nest fell apart so often I ended up reinforcing it for them with some twine when they were away! They came back and had two more sets of babies in the same spot.
https://www.wild-bird-watching.com/images/dove-nesting-on-la...
https://www.reddit.com/r/Ornithology/comments/6i7cwk/dove_la...
We had a pair in a planter box whose nest fell apart so often I ended up reinforcing it for them with some twine when they were away! They came back and had two more sets of babies in the same spot.