I really don't know when Masons are looking to nest but I would still put a block out.
Why can't you have honey bees in the city?
Quarter acre lot, residential. When I was researching all the chicken city codes, out of curiosity, I looked honey bees up and the city code specifically says we can't have them on lots our size. I'm not positive on the exact code, but I if I recall correctly, there was a requirement for land much, much larger than ours.
I have a friend who's parents own a pretty large bee farm and they sell all the bee box stuff - which intrigued me, not that I wanted to be anywhere near them while they were messing with the boxes. It was cool to watch from the safety of their store. I probably wouldn't do it anyway since I have small children (and chickens who are dumb enough to eat them - don't chickens get stung?)