You can also try to create a dummy building named "You can only have 1 such building" placed somewhere in the corner of the map. If you build the One-of-a-kind building, destroy the dummy unit (set that building on a Unit variable so you can kill/resurrect it depending on if the building is destroyed/rebuilt), obviously 1 dummy/player.
Unlike Meticulous's way, this will tell the players that Obvious Statement instead of just poofing the build button.