The roof is constructed of 1x6 sawn (undressed, unsurfaced) treated lumber.
You will need 220ft in random lengths for this.
Always cut the longest boards first, so the off-cuts can be utilized for the smaller boards.
Firstly, put two pencil marks (square off the board) 42" apart along the edge of one of the random lengths of 1x6 lumber. (See fig 8.)
On those two pencil marks, pencil another line inward at 20 degrees.
Set the blade on your circular saw to 11 degrees and cut along the pencil lines.
You now have your first roof board, and you will need eight at this length.
Cut the rest of the roof boards to the following lengths (the measurement being the longest point):
8@ 42" (already cut); 8@ 38 3/4"; 8@ 35 1/2"; 8@ 32 1/4"; 8@ 29"; 8@ 25 3/4"; 8@ 22 1/2"; 8@ 19 1/2"; 8@ 16 1/2"; 8@ 13 1/4"; 8@ 10"; 8@ 7"; 8@ 4";
When all the roof boards are cut, 104 in total, take the first board (one of the 42" longest boards) and place it on top of the rafters in a position so that the two ends are sitting on the center of the rafters and both ends of the roof boards are equal distance from the bottom of the rafters.
Temporarily tack this board in place and then proceed with the next 42" board, butting up tight to the first board and tacking to the next rafter.
Continue this action around the perimeter of the gazebo roof.
On the first boards only, a 1" thick fillet or packer will need to be inserted under the bottom edge of the board and on the rafter, in order to raise it to the same pitch as the rest of the following roof boards. (See fig 9.)
The rafter pitch is 40 degrees, but because all the roof boards lower edges are raised to sit on the roof boards beneath them, the roof board pitch will be more like 30 degrees.
When the first row of boards (the eight 42" boards) are in place with the fillets or packers inserted, (fig 9) and are all equal distance up from the ends of the rafters, and all joining in the center of the rafters, then nail them in place onto the rafters.
From here on it gets easier.
Get one of the next longest roof boards (38 3/4") and lay it on one of the first fixed boards so that the ends line up flush with the lower board ends.
Check both boards are parallel. Nail in place.
Continue this around the perimeter and so on, until all the roof boards are fixed in place.
The last row of boards (at the very top) might need a trim to ensure they fit snuggly against the hub at the apex of the gazebo.
Drill and screw roof boards together where the span exceeds 20".