a plain old optical builders level is not a bad tool, the biggest draw back is that it takes two people or you need to have your story pole/tape measure, up so you can read it and then mark it later, been using one for a good 35 years,
but for no more than I need it can not justify a laser unit, IMO,
for one thing the dot on the laser at 50 to 100 feet is a fair sized, and the cross hairs on the optical level are usually only about a 64 of an inch in thickness,
usually I can get the wife or a friend to help mark out the area when needed,
yes one has to be carefully not to lean or "manually readjust" the level when turning it, but by a quick swing back to the starting point one can recheck, your self,
my old water level I used before the optical level, was just a length of vinyl tubing, with a colored water in it, I would fasten one end up to a post as a given, and mark the tube on the end I had, (I had a mark on the tube) but with enough of the tube above so I would not force any liquid out when moving, from place to place (no air in the line),
then I would then go to a place I wanted to level and adjust the water in the tube by moving it up or down to the mark, on the tube and it would be level with the mark where I started, (if want to check I would tape the tube up and walk over and look at both to see if there was a change), if you did not spill any liquid or have any air in it to escape you could level that way,
even a string level is not that bad for a pole barn, put the level in the center of the string or it will not level out right, (as it will not adjust for the sag in the line off to one side, needs to centered).
if your just rough sighting in a string level is a fast and easy way to get fairly close, usually with in a 1/2" in 50 feet,
