Welcome Wallydog
I used the metric plans from angib
http://www.mikenchell.com/images/metricwarrior.pdf
Pay close attention to detail 1 and 4 without the offset on the hatch side walls you have a triangle hole in the side when the top is up.
If you use a hurricane type hinge you have to put a gutter on the open side of the hinge because they aren't water proof from both directions. I'd use a piano hinge with a rubber seal over the top on my next one.
The original design has the swing down hatch wall hinged at the bottom I'd recommend that you hinge it at the top. At the bottom you have to lift the top than lift the wall into place. Hinged at the top it swings down into place as you raise the top.
An idea that I'll use next time is to put a exterior door into the seat storage it tends to be a pain to move the cushions to get to stuff stored there so I don't use them as much as I would if I could put stuff in from the outside.
The build isn't as hard as it would seem. I built the sides in 3 sections, front outside, rear inner wall and hatch sides. Then assembled the front outside and inner wall on the trailer floor and put the top on the front. Than screwed the hatch walls to the front half of the trailer to hold them in place to put the roof on the hatch.
Hope that this helps and doesn't confuse you to much. I think that this is one of the most comfortable and practical designs out there but I am a bit bias.
If I can help in anyway just PM me.
Gary