I thought that an eyebrow dormer would fit in with the architecture of the house and garage quite well, so I started a little internet research to see how people had built them in the past. Most of the processes involved pencils and strings to make the radius curves, and often they were built on the ground and lifted into place once everything was test fit. There were many ways of framing them, some with rafters perpendicular to the front face and some with ribs. I decided that ribs would be the easier way to go, and since laminated veneer lumber, also known as LVL or the trade name Microllam, is available in large sizes, I utilized a piece of 1 3/4" x 24" x 12' LVL to form the ribs. Rather than the labor intensive pencil and string method, I opted for a 3D CAD model which I then turned into full size paper patterns like this.
The exterior trim is cut from a sheet of Azek cellular PVC. I had based the size of the dormer assuming a 4'x8' sheet of Azek, but later found that the local lumber yard stocks it in 4'x10' sheets and it would actually have cost more to special order the 4'x8' piece. I might have flared the ends a little more knowing that. I even laid out the patterns for the double 1/4" plywood sheathing using slightly larger top pieces to compensate for the plywood thickness.
Here it is with the ribs going into place.
This is what it looks like from the inside.
And here's the outside with the shingles and trim installed.
The gable roof is only about 14' deep and there is a triangular flat roof in back which is hidden from sight. Even though the garage is a trapezoidal shape, it looks almost rectangular from most viewpoints.