The order of the magnitude of the length in meters is estimated based on the average length of the object: if it is a small object then the unit would be cm and if it is a long object (like a road or something) the distance can be measured in km. Then we convert the unit we measured in into the SI unit of the meter.
Based on this, for the mentioned objects, the estimated length would be as follows:
a- ladybug: 10^-2 meters
b- your leg : 10^0 meters
c- your school building : 10^1 to 10^2 meters
d- a giraffe: 10^0 meters
e- city block: 10^2 meters