It is possible, though probably not the way you want it and with the lack of information I cannot provide you with additional detail (let alone the fact that I don't deal with PHP).
Nevertheless, Object Relational Mappers normally use an intermediate definition of the "Mapping" between the objects and the corresponding tables which also includes a definition of the relationships and indexes (indeces?). Although the purpose of this mapping is not to generate the underlying schemas, most ORMs provide a way to deduce (thus create) the underlying database. You could probably take a look at
Doctrine's schema as an example.
That said, I don't think you should use an ORM at all if your purpose is a one off generation of the database. What you should do, is give us more information of what you're trying to achieve, with examples.