If you want to create and update your Jenkins Job in some folder using Jenkins Job Builder (jjb), you need to put the name of the folder into the name of the job:
- job: name: "developer/zar/buildroot"
Note: at this moment Jenkins Job Builder isn’t able to create folder on demand by itself. This feature is not supported yet, but it will be sometimes, I hope. You can track the progress on this feature in Gerrit here.