They don't have a purpose, they are purely decorative. That kind of detail is often used on slate roofs in the UK , and I think it is because the slate can't be bent over a corner and something is needed, either concrete or metal, to cover those seams. When I spoke to someone in Louisiana about the tile she said there is a long history of tile roofing there, especially in NOLA. Ships bound for the port of New Orleans often carried tile in the holds for ballast. When they docked, the tile was unloaded and sold cheaply, as the space was then needed for outbound cargo. The tiles were plentiful and became part of the architectural vernacular of the area. Now many roofs are trimmed in tiles, both the barrel type we have and a V shape that fits end to end with a thin mortar line between. Ours are a 3:1 mix of charcoal and brown put on randomly. They come in a few other colors and it is amazing how a certain combination of colors looks just right on some shingles.

The current pediment slope of 12 in 12 is severe. There houses were modeled after English structures that were modeled after Greek & Roman temples that would be of considerably lower slope. The same goes for the gable or hipped roof slope of a Georgian or Federal (Adam) stye house. However, Colonial Revival houses often have 12 in 12 sloped hipped roofs that are truncated and capped with a very low sloped pyramid roof that can't be seen from the ground. This allows a much larger third floor area, less deep dormers and avoids the oddly French looking tall hipped roof. Show us some photos of the other houses. 1891 Colonial Revival house with some Victorian influences. photo of same 1759 Georgian house - HW Longfellow home & headquarters of G Washington "Longfellow National Historic Site, Cambridge, Massachusetts" by Daderot at en.wikipedia - Originally from en.wikipedia; description page is/was here. Original uploader was Daderot at en.wikipedia. Licensed under CC BY-SA 3.0 via Wikimedia Commons - http://commons.wikimedia.org/wiki/File:Longfellow_National_Historic_Site,_Cambridge,_Massachusetts.JPG#/media/File:Longfellow_National_Historic_Site,_Cambridge,_Massachusetts.JPG Federal house

Hip roofs (properly built and tied to the walls) are supposed to be stronger in high winds. One of the problems with gable roofs is the way they build them, with the studs laid flat. In our house, I doubled them up with studs turned 90 degrees, creating a very strong L-shape. I'm not sure why gable trusses are built that way, other than being easier to ship. A gable can be built to be just as strong as the flat walls below it. After living in coastal FL for 30 years, I'm obsessed with wind. I had my trusses built to a higher wind rating than required, used the biggest hurricane clips they make, beefed up the gable ends, and nailed my roof sheathing to FL codes. The inspectors were amused at my over-built roof.

Yeah, I noticed, lol. I even tried to filter by style, but Houzz doesn't actually know what architecture is, apparently ("Contemporary," "Beach," "Rustic," "Tropical," -- Seriously???) What I need is a huge architecture database. Or someone to watch my kids while I bury my nose in the local university's library for a few months.