@Hirnsausen I was just about to suggest basically the same idea, but I was imagining it working more as a "towing service".  I think in priority, it's more important to clear out the inactive users' constructs than to clean out constructs that have just been there a while.  I believe your idea works, but maybe the 7-day counter should reset if a user logs into the game.  So, if a users' construct has been within the "purple zone" for more than 7 days and they haven't logged into the game, their