In RTW, unlike M2TW, there is no way to delete a building. The only command that might be able to select a building card is the select_card, but I've tried and never actually got it to work. That being said to effectively destroy a building, but you could script it so that everyturn, after some event, the buildings health is set to 0, that means that it will always be useless even if the player rebuilds it.