Hi Steve, welcome to our little bit of heaven. Good, another woody in the making, and I am sure it will look individual. You asked about the construction of the hatch lid. In my case, I cut the sides to satisfy my needs, but didn't finish them off completely. Then I clamped a template to the hatch side area, marked it to fit the curve and transfered that info onto the hatch ribs. I morticed the hatch ribs into the upper and lower hatch members then installed the hatch lid plywood. After attaching the hinge, I applied the hinge and gave it a trial fit.
Sometimes there is a bit of spring back after the plywood is installed, and if so, the rear hatch sides can be altered slightly to make it fit perfectly. I hope this helps. You might want to check out my const pics below, sometimes a picure is worth a thousand words. Good luck on your build, remember Wood is Good.

Roly