I have a 30 x 40 shop and want to add a roof awning to one side. I can get 2 x 6 x 20's for rafters? So here is the situation, roof structure slightly sloping, 40 foot deep and 20 foot to the side. (Slope will be the 20 ft direction) Thinking about telephone poles for posts, maybe 4 on the 40 foot span? Spacing on roof joists for the number I need in the 40 foot direction? Metal panels 3 foot wide and 20 foot long. Number of 2 x 4 x ? cleats to screw the tin on and spacing 20 foot direction? Guess this is mainly structural question to carry load of roof.

I don't think you can get 20' 2x6s very easily. Why don't you set your post back 2' and have a 2' overhang. Then you can use 18' lumber which is easier to find. As far as spacing 2' oc is the norm but if its only holding tin 3' oc might make it easier and you are going to need some blocking at that length. I am not sure of the load values of a 2x6 on edge.

Yes, 20 footers are few and far between but there are some Home Depot stores that have them. Wondering if i should put another set of poles for support. Maybe extra set at 10 foot for weight load to support 20 foot span?

I would have to run calculations for load, and I don't have the time right now ... but probably can find online calculators to do that.

when I was reflooring my 20' gooseneck trailer, about the only place I found that had 20' lumber worth a darn, was 84 Lumber. McCoy's had some but most was very warped and crooked on the 20' length ... but did use them for a 16' trailer. Couple of other options over Home Depot for you to check out.

Do not forget about sawn telephone poles. The place in Bowie, they have long pieces of lumber.

By any chance have a name for them?

Stice sawmill, Bowie.

I don't know much about using wood for that length run, I'd use metal c channel / pfc.

By their facebook page, they have closed.

My garage is 24x36. I spanned it with 24’ 2x8 SYP from HD. Go to contractor desk.

2x6 won't span 20 feet without sagging , if you figure in any kind of load need at least 2x10
If you halve your span with another set of posts and a doubled 2x8 beam 2x6 would work.

2x10 more better. Do it right the 1st time.

x2. I used to go wood on everything until I got tired of building it twice.

Agree on metal. Been there, done that too many times with wood.

C Beams is definitely the wayI would go also !!!!!

this, you will also have to use bridging blocks at least in the center, I would do 2 rows on equal spacing.