stephen,
You're in luck. I just finished building an 8' x 16' hard top for my 24' pontoon boat. Here's a picture.
It is all aluminum secured with stainless steel bolts and screws. The six verticals are 1" x 1.5" x 1/8" thick rectangular tube 7' long. They are secured to the fence at the top rail and the bottom of the fence. The frame for the top is 1.5" x 2" x 1/8" thick aluminum angle with gussets at each corner. The cross members are 1.5" x 1.5" x 1/8" thick aluminum angle. The top is two 4'2" x 16' sheets of a corrugated aluminum material called Fabrib.They overlap in the center and are secured with about 100 self tapping screws. The top is reinforced with support rods made of flat aluminum that tie the verticals to the fence rails at two corners.
My plan for lowering the top for towing is to remove the bolts from the bottom of all six verticals and allow the verticals to pivot forward and down. I deliberately left room at the top and bottom of each vertical to keep it from binding while lowering. I only erected this a few days ago and I have not lowered it yet, so there is more to be learned. I suspect I will need some vertical supports on the deck of the boat to hold the roof at the right height in its lowered position. I'll likely also need some straps to keep it from moving about while being towed.
The bolts at the top and middle of each vertical are secured with Nyloc nuts so they can be left just loose enough to allow the top to fold down. The bolts that secure the bottoms of the verticals screw into rivet nuts that were installed into the fence rail. That makes it easy to put the bolts in and out without having to move the furniture to get to the backside of the rail.
The bad news is that I have not yet tried this top out on the water. It seems sturdier than the canvas top it replaced, but I won't know for sure that it is engineered correctly until it passes its sea trials. If you don't start your project for a few more months, I should be able to report back on how it worked.
