Boolean not working corretly, it's making my main building dissapear!

Hey guys,
I’m having a small big problem here.
I want to cut the object “cutter” from the base main building, but the main building dissapear and just cutter stay there. Can you guys check or help me please?

base.blend (443 KB)

Clean up the house mesh

Get rid of all the internal faces and fill in the holes

internal faces

Just one of the holes

Hey , thanks! But i did that steps and it still disappears, i don’t know why

base.blend (444 KB)base.blend (444 KB)