understanding rafter span charts

[sedgwic]

I've decided to build a roof at 9/12 pitch over a 16' wide (24' long) building. I want to use a ridge beam supported at each end to make a vaulted roof. I have access to 2x10x26 for the beam, which would allow me a foot off of each gable end. The bottom length would be approximately 121" from the beam to the top of the bird's mouth. Using the #2 SPF **** from Lowe's I'm thinking I need to use 2x8s for the rafters and 2x10 for the ridge beam. I'm having trouble making sense of the span charts (and calculators) to ensure I've chosen right for the rafters. I think, from what I've seen, that 2x8 rafters would span over 13 feet at 24" o/c.
I live in Raleigh NC where a foot of snow is possible but highly unlikely. I was planning to use 5/8 T&G OSB for decking and then screwing down corrugated metal roofing on top of that.
Anyone want to tell me I'm heading in the right direction or screwing up?

 

[Cyberbear]

It might be a good idea to run your ideas past your local building dept. Since they work with this frequently, they should be able to answer your questions. Wish I could help more, but I'm on the west coast and requirements are different here.
I remember building a vaulted roof/ceiling a few years back with a 25.5' ridge length and needed a 6 x 14 beam because there were no rafter/ceiling joist ties being used. Unless there will be support posts under the 2x ridge, you need something that can carry the roof weight, and not bow out the exterior walls.

 

[sedgwic]

Wow, gulp, that's a massive chunk of wood.
Technically, I live in a little town south of Raleigh. I have already written to ask if I could run ideas past the building inspections dept. I got no reply. I guess I need to go down there and ask in person. we want to have max height inside and have already acquired 105" studs. I may have just do this with collar ties that were discussed in a previous thread I wrote about this.

 

[kbs2244]

With a ridge beam construction the rafters are in tension, not in compression as in ridge board/joist construction.

I would plan on using the metal joining plates at both ends.
In addition to extra strength they just make the joining easier.

This PIC shows a common hybrid.
The steel is structual and the board above it is just there for the easy joining of the joists.

(The screw jack post is there for temp constuction use only.)