Framing longer walls for garage/shed.
I just finished pouring my own concrete slab thinking the internet provided free plans would be enough but I am stalled without better knowledge.

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The walling is nailed to the uprights - I guess your using siding material or ship lap. Cut them at a convenient upright so it comes half way over then nail the next one up to it in the other half of the upright.
In the UK we usually look at about 18 inches between uprights with noggings nailed between them to separate and make a grid.
A floor plate and roof plate will complete the frame then sheath with the siding material. Even your 16 foot wall will need more than 1 board??
Rick, I am building either a large shed or small garage using 2x4's trying to get out as cheaply as possible. Although I can get 16ft length boards, I do think you are right that even the 16ft wall would need more than one board so I need to plan accordingly.
Now that the hurricane is passed I can get started!
In your opinion, would a gambrel roof be something I should try as a novice? Or should I stick with the more traditional gable roof?
Here's a pretty good start - and it's an instructable to boot. The top plate should be doubled though. if your lumber won't span end to end of the wall you can splice the top plates. put the splice over a stud and don't splice both plates at the same stud.
Google "garage framing" "house framing" and other similar keywords and read up a bunch. Take what you see with a grain of salt.
Visit some houses under construction to get more ideas of what's supposed to be going on.