Probably you have to use customized game mode instead (If I understand it right). If you want to create match-wide randomness you have to create a custom game mode BP. It is a bplueprint with base class of GameMode or GameModeBase. GameMode will better if the default behavior is good for you. In this class you have to create an integer variable for game-wide seed and fill it in a construction script with random value.
Then you have to modify a construction script of your building
and generate a building based on the stream stored inside an RndStream variable.