Building cost when fast building

When fast building a building with human, how much does it cost to fast build per worker?

I know that every worker increases building speed by 50% but how much more does it cost per worker?

Solution 1:

1 gold and 1 wood every second for every additional worker.

Solution 2:

Excerpt from the liquipedia wiki

Powerbuild Cost :   0.15
Powerbuild Rate :   0.6
Repair Cost Ratio   :   0.35
Repair Time Ratio   :   1.5

This suggests that it costs 15% more per worker to finish a building.

So 5 workers on a town hall makes the town hall cost 60% more.

I'm going to test that soon and confirm here.