An easy way is place a known next to the building. The known can be a person and you know their height. Of course how exact does come into play with the final outcome. Next, step a distance away from the person next to the building. Either use your thumb, pencil, ruler or some means of measuring the person from that distance you are standing create a point of measure for reference on that measuring object.
Then find a reference point on the building at the height of the person standing next to it like a line or bricks or a something. Now, slide your marked measuring tool upward until the bottom is at that point. You now have two measured distances or 2 times that persons height. Repeat until the total height of the building is reached. The count of times the measuring device was mentally stacked upon itself at the building multiplied by the known height of the individual is the total height plus or minus maybe a foot.
Or, go to the top and drop an object. Time the fall until say the egg spats or the balloon full of water. An object falls at 32ft per second per second minus the resistance of the air or wind.