Well I was on the roof shingling and I was walking around and the roof made creaking noises...

Welcome to AMHD

Can u give more info?

Is there movement of where u step and how much?

How many layers of shingles on roof? What type of shingles?

What is pitch of roof?

Size of rafters and thickness of sheathing?

Answer these questions and we will be able to help u.

Chuck

And you went up into the attic and looked at the truss and the underlay wood, what did he look like?

the time to replace the plywood would have been while you were shingling. If you are really concerned you could brace the plywood by in stalling 2 x 4's between the trusses or rafters from the attic. To replace the plywood you need to remove the shingles and underlayment, replace the plywood and install new shingles that may or may not match. If you did not fall through while shingling or walking I would not worry too much about it.