AoS Using the Kroxigor Moonhammer versus Garrisons

I think that's the name of the weapon. Anyway, how do you rule on this?

 

Do you mean how many can be hit?
You can attack the unit inside the building the same as normal.

I haven't run into this but I would put the occupying unit down on the board somewhere and fight the battle there.
The unit should of course be restricted by the dimensions of the buildings walls.

Then whack down a Krox and measure to see how many you can hit.