I'm building a new shed, 12' wide and I want to do a 7/12 roof. Do I need a ridge board? Do I need to use 2x6 or will 2x4 work for the rafters. Explain to to me like I know nothing about carpentry please.

Thanks

Have you considered just buying them? You can get 12ft rafters from your big box lumber stores. Otherwise there are videos on you tube that would be helpful.

I looked at a span chart briefly and i would go no less the 2x6 for rafters. With a heavy snow load 2x8 might be better but with your 7 pitch it will probably ride. You will need a ridge beam. Old schoolers used a 1x but i think a 2x is better as well as it being deep enough to capture the whole cut of the miter on your rafter. I think collar ties are good too. Essentials the board going from one wall to the other horizontally capturing both rafters and wall. When loaded the roof wants to collapse and push the wall outs. Collar ties resist this force. All said if you nail and brace well 12’ wide is pretty minimal. Good luck

I would use 2x6 rafters, and a 2x8 ridge. 24" centers, 5/8" plywood.
Use NAILS, not screws.
Do yourself a favor, and get what is called a "speed square", which will make your ridge cuts simple.
Seat cuts, (the part of the rafter that sits on the wall), are a little trickier. For a shed, I would just not bother, and use H-1 Simpson brackets, and 2x6 blocks, (22-1/2"), between the rafters.
You can make collar ties, or span wall to wall with 2x material for ceiling joists.

Thanks guys. I made the side walls from 2x4, 16" on center, is it okay to put 2x6 on top of the 2x4 walls?

No point, you only need 1 inch of bearing, and the overage will be unsupported anyway.

This is what I got so far. Its a 12x18 which falls just under needing a building permit. Floor is sandwiched between 3/4 green treated and insulated. Putting 3.5' barn doors on the front so I can bring in my small equipment to work on.

first question what is your snow load ?
typically your building code will tell you what snow load you need to build for you area.
then you can drop that info in rafter or truss calculator.

you actually go wider than the 12 feet because you want some overhang but given a 7'6" interior height and an interior width of 6 feet your looking at about a 15:12 pitch roof.
I assume you are doing this to get attic space for storage , you probably want a gamble roof a "barn roof" this gets you more useable space and typically you build them as trusses so then no ridge pole is necessary

I was imagining no real ceiling, just leaving the inverse V more less and not running a board on the bottom of the truss or top of the wall.

Edit. If I'm trying to do something moronic please tell me, I've never done this type of work.

With snow load there's really no way around 2x6 and 2x8 ridge, 24" or 16" oc. Up the plywood to 5/8 or 3/4 if going 24"oc and 16" is iffy for 1/2. You will also need wind ties and or ceiling joists as well.
One advantage of ridge vs no ridge is that each end of the ridge is fully supported at the end walls carrying the load of all of the rafters.

Now down here without snow 2x4 without ridge 24"oc would suffice with good wind ties, I would scab plywood triangles for wind ties. But I would still use 2x6 with ridge.

so your doing this to get a high ceiling to mount your skinning rig from?

you want a tie from side to side about every 6 feet or your inverted V pushes out the walls

at 15:12 you wouldn't keep much snow on the roof that is for sure

so you need to answer some more questions , how long is your building? you said 12 feet wide

what type of roof do you plan to put on it , metal , shingle , shake ?

a book that might help you is . A Graphic Guide to Frame Construction

You really need the joists or wind ties. If you can picture it, the weight of the roof is pushing straight down. An inverted V wants to spread and flatten. Without joists at the wall top or ties further up the rafter the walls will eventually bow outward and fail. The taller the rafter the lower the tie needs to be without joists.

The only other bracing that'll offset the bow is internal cross walls with sheer bracing, such as being sheathed with plywood. But even then the roof can still move off of the top plate as only the fasteners are holding.

The building is 20' long. Hoping to do metal roof

If I put a small loft in the back say 6 feet of the building would that be enough to keep it from being pushed out?

I think I'm starting to understand what you guys are trying to tell me. I could still have no ceiling but have a 2x6 across every 6' the length to hold it all together. I was hoping for the high ceiling to hang all my antlers and skulls up there more than anything. Also hoping the snow would fall off without needing to go rake it

metal roof or shingle roof?

exactly and since it has no weight bearing you can actually use a 2x4 although a 2x6 would let you hang more stuff from it

also are you finishing the ceiling , insulation ?

Metal roof and it will all be insulated