I will put that on our todo-list This wasn't implemented in the Java version because this information wasn't available yet (the server which triggered the event didn't even know how much stone or lumber was required for that blueprint)
But we need to add this information anyway for survival mode (so players can no longer place blueprints "for free").
Not sure about individual methods though (like event.getIronRodResources() etc) There are so many potential items that could be required, so maybe we find a more abstract way to expose the resources in the API.