Should I Measure Myself?
We would strongly recommend that you don't. If you get out a tape measure in order to determine the sizes you are, you will almost certainly order sizes which are too large, or too long, because you will not have the experience to interpret the tape readings.
Establishing sizes doesn't have to be over-complicated, since most people already know their off the peg sizes, and also a lot of the clothing people wear will have a size label in that tells them all they need to know. All that needs to be done, is to compare how an item fits them, with the fit that they would want from a wedding suit, and to make the necessary adjustment if they think they would need to. E.g. If a pair of casual trousers fits well but is a little "bunchy" on the shoe, then take one or two inches off that leg size when ordering a formal wedding suit.