Hey Zipline, Welcome. You will find lots of good ideas here and helpful folks as well. Here is a 5 x 8 that was built for off road use by a very handy young man. Check it out, you may get some ideas. viewtopic.php?f=42&t=70018
I have a 5'x5'x12' that I first built one way, came back from a 2 month road trip and totally changed it. Your best bet is to decide what you want to use it for and how you want to use it. I know that sounds obvious but I had a nice aft galley and fold up bed but ended up not liking either.