Framing a pyramid hip roof?

[MushCreek]

Heading off on a completely different tangent, I happened to draw up a square house. It looked good with a hip roof, which is a pyramid on a square house. I was trying to figure out how to build it. I guess you would put up the hip rafters first, but they're kinda big- about 25' with the overhang (the house is 28 feet square). How would you hold them up? Can you even buy 2X's that long? I suppose you could build a big truss for the first diagonal, and then attach the other one to it. I looked it up on-line, and every article dealt with a hip roof having a ridge, and that's where they recommended starting.

Would you double the hip rafters, or bevel a single 2X, leaving only 3/4" to fasten the sheathing to?

How would you connect the 4 hip rafters together in the middle?

I know a hip roof is theoretically self supporting, as long as the corners can't spread. What about collar ties? I would have joists to attach the ceiling to; would I tie them to the jack rafters?

How do you put a tin roof on a roof like this? Or any hip roof? Wouldn't there be gaps under the ridge caps from the ridges in the tin? I would think wind could drive rain under there pretty easy.

I don't know if I'll build this design (or any design, for that matter) but I thought it would be interesting to discuss.

[MountainDon]

I built the roof on our gazebo by beginning with a 4x4 that was placed at the peak where the four 2x6 hip rafters meet. First one pair connected to the 4x4. When that was up and temporarily braced I installed the third and then the fourth hip rafters and nailed it all in place to the yop plates. But it is only 10 feet square. 

[Don_P]

Never framed a diamond hip, I did remember it in will Holladay's book. He frames it by first placing the king common rafters, the 4 from the center of each wall, then installing the hips.

code says you have to support the peak or have it engineered and that hips and valleys be designed as beams. You are correct that if it is built as trusses or if the plates form a tension ring that would work. If at all possible I prefer to make hips and valleys out of 2 plies and bevel each.