Each of those examples calls for more than just a barometer:
a) Measure the height of the barometer, and carefully laying it end to end on the side of the building, find how many barometer-lengths high the building is.
Requires the barometer, some type of measurement device, and a ladder or other way of scaling the building.
b) Measure the length of the shadow of the barometer and the length of the shadow of the building. Using proportions, work out the height of the building
Requires the barometer and some type of measurement device.
c) Locate the custodian of the building. Say to him, 'If you tell me how high your building is, I'll give you this barometer".
Requires the barometer and a custodian.