I have a deck on the front of my house, it is 31 feet wide 16 feet deep.
I have decided to enclose the deck and put a roof on it, just make a big enclosed covered porch.  I found a guy to help me frame it out  and he has 35 years’ experience building and seems to know his stuff.
To match existing roof lines the new roof will be a 4-12 pitch hip roof.  
The common rafters will need to extend the wide part of the porch, the 31 foot portion.  This contractor said he would use 2X6's for the commons 2X8s for the two hips.  He also said the ridge rafter could be a 2X6 because it isn’t structural, he said it is just to line up the commons.

My question is, are 2X6's adequate for 18 foot commons?  I am in SW Oklahoma and there is no snow load.
He also said we would do 24 in OC and he said that would be good.  I thought 16 OC would provide more strength?
He mentioned collar ties but didn’t say anything about rafter ties for the lower third portion of the rafters.  I would think these ties would be crucial to prevent the walls from bowing out?

30 views and no comments or suggestions, I thought this was a tech/help forum?
Do any of you guys that have a contractor/carpenter background have any input?

first you need to find out what the building codes are and start from there. im having a hard time picturing this, pics would be nice.

There are no building codes or permits required where I live.  Picture some place very rural and then go even more rural, thats where I am at.  We are talking gun range in the yard type rural.  I checked with the county about codes and permits and they laughed at me.  I'll see if I can find a pic or something.

Here are a couple of pictures to try and expalin what I am talking about.
I have a false hip like this.


Now picture that hip roof to be 32 feet wide.  What I want to do is bring that 32 foot wide hip out about 16 feet to cover my deck.
Something like this (its not to scale)


The guy is telling me he plans to use 2X6's for the commons.  The run on each side is going to be 18 feet.

That's a pretty big run.

I would be more comfortable with 2x8's.

I think I would go with 2x8 ridge, 2x8 common, and 2x4 collar ties.

If I got into 2x6 commons I would be plating with 3/8 ply.

Call the lumber yard that would be your supplier.  They should have a rafter span chart that figures snow load for your area based on they species of wood you will use.  2x6 24" o.c. sounds light to me for that span.

Thanks, since I am paying for this and helping the guy in the process I am calling him and telling him I want 2X8's.  
Is 24 OC ok or should it be 16 OC?
He gave me the materials list to buy and told me to get true 1/2 inch sheathing either OSB or CDX.  Is one stronger than the other?

I like a roof strong enough to have a dance party on. 2x8 16" centers all around!

CDX should be stronger, but OSB is getting to be pretty good quality. Not what it used to be.

2x6 #2 southern yellow pine rafter @ 24" oc and l/240 good for only 12' 3"

per American Wood Council span calculator.

2x8 same specs good for 15" 10".

Try it out

http://www.awc.org/calculators/span/calc/timbercalcstyle.asp

I looked at the AWC calculator earlier, thats one of the things that had me second guessing the carpenter.  
Plus the fact that in my own head 24 OC 2X6's wouldnt be a good choice for 18 foot common runs.
The calculator does show #2 southern pine 2X8 can span 18'6" if its 16 OC which is what I plan to do.
Thanks

I agree with the other guys.  When I covered my patio with a roof, I used 2X8 fir rafters for the 12' long roof rafters.  

Personally, I thought that was about the limit for 2X8's.  If I could have worked it out, I would have used a deeper rafter.

I would not use 24" OC, either.  Go 16" OC.

Not to be picky but your horizontal span is only 15ft 6in not 18ft.

good luck on your project

I used CDX on my roof because I can't stand OSB however the OSB is  half the cost of CDX

You're right, we were just using the 18 foot length thinking thats what we would get and then trim to right length.  Still, I dont want to run 2X6's 15'6".