From time to time, I do run tests in order to understand how this game works. Some of those tests may interest you, only because of the data, since I do not add any conclusion.
This is a test about barracks and the influence of adding a new one, https://bit.ly/test-barracks.
For some reason, this test shows a crazy cost increment for level 27. I suspect it's due to Training cost III technology and the fact that 27 crossed the 25 building milestone. This would mean that building levels are related to Training cost and speed tiers. Being Barracks 25 related to Training cost/speed III.
Something more, the cost per 100 units kept growing when leveling up the test barrack. This could be related to the leadership and dominance being trained. If that's true, both leadership and dominance have a significant weight in cost, and it would mean that, when the barracks are not at the same level, the final values trained are averaged.
I had some previous tests about clan management and clan resources, but is far better if you join a big clan. In case you were interested in those tests, let me know through the game chat. Currently, Kingdom 70, clan [DoD] NV, player LambdaEdge.
Those tests require having some control over the clan, superior or leader, and also creating spreadsheets. Here is an example https://bit.ly/shc-status