root vs root-build

When I import my play product into Idea, I get two modules in Project Structure.

What are these? root seems to have, pretty much, what I would expect.
But what is root-build?

Even more confusing are the Problems section with:


I'm not clear how to deal with these. This occurs right after importing the project.

Then theres the SBT, SBT Runner and bewildering set of Scala options.
Some explainations would be helpful.

All of this and no class files seem to be generated.