Hey there, I'm trying to learn some basic modeling on my own using SolidWorks. So here's a scenario that I'd like some help with. 

To practice, I opened up an old cell phone, took the board out and started creating a model of the board so I could use it as reference for a new case design. I've got the board done as a part.  Now I want to start making the new phone case, how do I use the board as reference to accurately model around it?

Or similar scenario, if I finish the top half of the phone case, how do I use it as reference to start the bottom half of the case so they fit together accurately?

Hope this makes sense, an answer to this would really help me get started.