I have a rental house i would like to replace windows in, several are
identical & i want to start there. What I would like to know is how I should
measure what i need to buy without exposing existing framing. I am assuming
I can simply measure the outside of the trim & the inside of the trim & buy
windows with a RO size right in middle of that +/- a little... is there a
particular brand or type that i should use or stay away from?

Thanks
Rob