Based on your statement, you've having problem with creating unit, not with capturing building system, is it ?
A test map is attached
It contains auto-create unit system (doesn't contain any capturing building system in it)
Simply load the test map, the instructions will appear right when you start the map
If you pressed ESC and if the Peasants are still lazy, just spam press it until it gets to work (this is because the Barrack has collide with another barrack, I just set the building location to random around the Peasant unit, that's why sometimes the building location is colliding with each other, making that Peasant disobeys us)