It i not my site. I just used it as a base when I was building mine. I did not follow the details of the build. Just used it as a place to get ideas when stumped.
When I mounted my wall I mounted a 1x4 cleat on the edge of the floor with screws from below before mounting the floor to the trailer. When building the wall I left the bottom board out so the wall would slide over the cleat. I had the outside skin go outside the floor and roof. Then trimmed the wall skin to the roof. I also left out the 2x2 frame and just put 1/2 foil covered insulation under the floor with little plastic pipe spacers where the hold down bolts are. I did not follow the normal ways.





click on pictures to enlarge
I also layer the ceiling on top on the walls then the ties and insulation and finally the roof. I also built the hatch as part of the main box then cut it off.The hinge mounting board and a board to cut in half was planned when putting the wall together. ((Not the normal way of doing thing))
Now look at the other builds and go what ever way you want there is no one way to build Just pick what ever way you see as best.
Good luck, Have fun.