Green roof for a brick bread oven

Hello!

We've started to build our brick bread oven. The concrete foundation is ready and the design in place, in the Spring we'll start on the brickwork. Everything is decided apart from the roof.

Inspired by a roof topped with thyme I'd seen on Dan Lepard's website (Jack Langs?), we're considering doing something similar. The question is how to do it?

Can anyone help to point me in the right direction? e.g. resources on the internet, books, or personal experiences.

We'll tile the roof if this doesn't work out, but it seems like such a great solution.

Many thanks in advance.

Joss