When working with drafts in 2c8 you can not create breakdowns of objects. That's because the model does not yet belong to a repository, and is not yet placed in a structure of models. To be able to make a breakdown from a model in 2c8 Lite, the model needs to be sent to a repository organizer that will place the model in a repository. After that, you will be able to create breakdowns in the model.
In this FAQ you can read more about sending a draft from 2c8 Lite: Where does my model go after I send it?