Google cloud storage using Java. If there is a specific issue or problem you are having getting one set up, post you code and any errors and we can try and help you sort things out. 

That is such a broad question for what would certainly be a very big project.

If you are serious about it, you really need to start by asking yourself a lot of very specific questions that don't have anything to do with the language you will use (Java in this case).

Once you have a very clear and specific definition of what you want to build, you will be able to ask specific questions about how to implement your specific requirements using Java.