Supervising other peoples work - an etiquette question

Hi
I am having all my shingles replace on my roofs.I am not doing it myself, but do know a thing or two, and have very high standards in what I expect of such projects.
I was wondering, if I worked at home on the day it was being done, if it would be ok to check on the workers every couple of hours to supervise the work, or would it be rude and insulting to them?
I am asking home owners and pros, and would like to know how to deal with the situation.
thanks

I have checked up on roofers before, cause who knows how long the employees have been working for that company.

Unless you know of work they already have done, its a good thing to check up on them. I would not stand there and watch them for hours at a time, But these shingles are to last 10 - 20 years, so you want it done right.