Actually rocket arty in general isnt the best tool for anti building... if you wanna take out structures use howitzers... otherwise the stuka is the best at the single role of building destruction
Stop repeating that rubbish.
Using the factory building next to the left VP on Essen Steelworks as a target, it takes:
2 volley from a Land matress at max range
2 volleys from a Katyusha at max range
3 volleys from Calliope at max range (Though the second volley brings the building well within 1hko range from any tank shell or mortar shell)
4 volleys from Stuka at max range
6 volleys from a Panzerwerfer at max range
HOWEVER, the caveat is this: A vet 4 Stuka can one hit kill a building for 100 muni using the incendiary barrage depending on your luck by setting it on fire.
It is extremely important to note. I chose the biggest building LENGTH wise and 3 of the rocket still lands far enough away to not do anything. If the building is smaller, it would take much more effort to kill it using the Stuka since even more of the rockets will be totally wasted.