The last step for a roofer is to check if their are any leaks in the roof. To do this a roofer typically uses a infrared camera to take a picture and check for areas that are leaking. They then use a moisture meter to find the exact spot of the leak and trace it back to the membrane.
A moisture meter is a must for a roofer, a leak in the roof can cause major problems within the structure as well as a fire hazard, health issues (such as mold), safety issues etc. A moisture meter is the only tool that can trace a leak back to its membrane making it an essential tool for roofers.