I would like for there to be a way for players to build and destroy only shop signs. It could be a subflag for the build flag. I would also like a way for the player who has created a shop on another person's residence to have access to that one chest.
This is a good one, although I don't see how it would be done. Perhaps a player should simply be able to access all their self-placed chests, if they have destroy flag?
I assume it could work similar to how the access sign works, however that works. Checks whose name is on the sign and give them access. Your idea could work too.