Entity Framework Code First will build the database for you if it doesn\'t exist and structure it based on your mapping objects. I believe Roundhouse will do the same thing
hibernate does if you set hbm2ddl.auto to create or create-drop or update in the config file. Using Java that is, I assume its the same for nHibernate.
If an ORM does not do ddl, there is not much point in having it, well its a key feature at least. Imho.