This is the one job where a laser measure is not simply faster than a tape. It does something a tape cannot do at all, and it does it from the ground.
Stand back from what you are measuring. Shoot the top of it, then shoot the bottom, without moving between the two readings. A tool with an angle sensor knows the angle of each shot, and from two distances and two angles it solves the vertical distance between the points.
That is indirect measurement, usually labelled as Pythagoras mode on the tool. It works for a ceiling over a stairwell, a roof eave, a gable peak, a tree, a pole, a building.
Units with an inclinometer measure the angle for you and both shots can be at any angle. Units without one require you to take one leg perfectly horizontal by hand, which is far harder to do accurately and makes the whole method much less reliable.
The failure mode is that the tool always produces an answer. It cannot tell that you moved, or that you hit a gutter rather than the roof edge, so it does the arithmetic on whatever it was given and displays a confident number.
Moving between readings is the most common cause of nonsense results.
Hitting the wrong thing. Aiming at the top of a wall usually means aiming at whatever sits on top of it: guttering, a light, a soffit, a pipe.
A drifted tilt sensor. This one is insidious because distance readings stay perfect while every indirect calculation is quietly wrong. Bosch quotes levelling accuracy of plus or minus 0.2 degrees on Blaze units with an inclinometer, and if yours disagrees with a spirit level by more than that it needs recalibrating. Tilt calibration is covered here.
Extreme angles, from standing too close, which amplify every small error.
Before trusting this outdoors where you cannot verify anything, test it somewhere you can.
Measure a ceiling height indirectly, from across the room, then measure it directly by pointing straight up. If the two agree, your technique is sound. If they do not, the difference tells you how much to distrust your outdoor numbers.
It takes a minute and it is the difference between a mode you rely on and a mode you hope about. Do it again after the tool has been dropped.
Worth knowing, because they work and cost nothing.
The shadow method. On a sunny day, measure the object's shadow and simultaneously measure the shadow of something of known height, like a stick or yourself. The ratio of the shadows equals the ratio of the heights. Simple, surprisingly accurate, and entirely dependent on sunshine and flat ground.
Counting known features. Brick courses run to a fairly consistent module, and standard storey heights are reasonably predictable, so counting up a facade gives a workable estimate.
A phone inclinometer plus a distance. Measure your distance from the base, use the phone to get the angle to the top, and the height is distance times the tangent of that angle, plus your eye height. This is exactly what the laser does, done manually.
These are estimates. Good enough to decide whether a ladder will reach or to rough out a quote, not good enough to cut material from. Measuring a whole building is covered here, and the indirect mode in full detail here.
Everything on LaserMeasure is built the same way, from owner reports rather than spec sheets. The front page is the summary.