The problem, then, is establishing plumb (or level) over distances much greater than the length of your level.
The solution? The on-site level lengthener.
Sort through your woodpile and find a straight piece of stock (sight down its length, as you would the barrel of a gun). Cut it to the approximate length you’re trying to plumb or level. Then tape your two- foot level (electrical tape will do as it’s thin; duct tape probably won’t because it is thick enough to add to the board a margin of error you don’t need). And Voila! A longer level is born.
(Check it before you use it, though, in case the milling on the piece was less than perfect. To check it, find a level surface with your level, then turn the level end-for-end. Does it still read level? If not, you’ll need to shim the level where it’s mounted to the lengthener, perhaps with building paper or cardboard, until the bubble is dead center.)
You can get fancy, too, and fabricate a more permanent model. If you do, you should probably use a very stable wood that won’t warp, or a piece of three-quarter-inch plywood, perhaps with solid wood edges glued to it.
This is a simple solution to a problem that will help make raising that wall, or whatever you need a longer level for, easier.