With a fix number of buildings that are able to convert and an appropriate amount of time and work you have to provide... and it would be a great base for user-driven content like "tradehouses", "hospitals", "dont-get-to-close-or-you'll-be-dead-houses"... And the ability to lose your house gives the pvp at least one good reason to happen. Maybe the building turns back to standard after a while when no one is doing maintance n stuff.