I have to be a partypooper,
If there is a door, and you buy a lock to lock it, then to lock has to be like an old padlock, becouse i doubt any of your characters are locksmiths that can all of sudden install new proper lock on the door and its frame
Picture in spoilers
That would mean that if you enter a building, you will lock it from inside which means that people that are outside have no way of lockpicking that. Their only option is to kick the door in, pretty much.
Of course if you lock it from outside then it can be picked.