There is a guy by the name of Patrick Remington on YouTube who decided to build his own. He has two versions currently on his channel, one being clamshell style, and the other being the more boxy style, like a James Baroud. At some point he started getting enough questions, comments, and ideas that he created a Facebook page for DIY roof-top tents. It's the only reason I have Facebook at this point. His are done with wood and epoxy, but some of the others on Facebook are modifying roof-top cargo carriers or doing more of a fiberglass method. It's well worth checking out.