I live in flats on the first floor, with people below and above me.
About once a week I have to endure the smell of weed coming in to my bathroom/toilet.
Should I report it to the landlord or police or do nothing about it?
I wouldn't want to get them in trouble or make them homeless but you're well within your right to do so.
Maybe a better solution would be to ask them or get a friend to ask them to stop/insulate their room better?