Davkrat
(By the way is Dave your first name?)
There are many different ways to attach the spars. Because of tight quarters and working by myself, I've had to build my teardrop in components, and then assembled them later.
I built my roof somewhat like others have built their hatches. My roof fits in between my sidewalls. I used a parallel 1 1/2" wide, 3/4" plywood "nailers" along on each side profile. For spars, I used 1x2 poplar - 12" on center for most of the roof; 8" on center at the tighter curves. I did double up the 1x2s on the only flat part of my roof which is at the vent fan. The spars were attached temporarily to the nailers with two 1 1/4" pocket screws at each joint. Then I fastened my 1/8" ply for the ceiling side of the roof (and hull liner too.)
The roof assembly was put back into place and held with clamps to the sidewalls. I removed one of the two pocket screws at each joint and replaced it with a 2 1/2" ceramic coated pocket screw that went through the spar into the nailer and into the sidewall framing. I then took out the other 1 1/4" pocket screw. From the outside of the sidewall, I used a 2 1/2" screw that ran through the sidewall into the nailer and into the spar.
Planovet (Mark) also built his teardrop in components and assembled them. He used a method similar to the one Steve Frederick's guide (worth every penny of the purchase price if you don't have one already.) Mark's website illustrates how he built his teardrop and is an excellent source as well.
Tom