I"ve never walked up to Andy Roddick live, so will defer.
He's listed at 6'2", and when he loses to Fed, he's taller than Fed, and 20+ lbs. wider in shoulders and legs.
I'm 5'10", and with insoles in my tennis shoes, might be close to 6', but serve like a 5'9" tall person just the same. I can't create the ball speed to exceed 105 mph, unless it's hot outside, no wind, no sun, new Wilson balls, and I"m fresh. Those are unrealistic conditions, for all to come together.
US Army test, Feb., 1980, I was listed 5'10" and 3/4, me making arches in both my feet, cheating basically, since I"m flat footed.
I"ve seen plenty of shorter players with MUCH bigger serves, but those guys are 4.5+ level players, and choose to spin the ball IN at barely 100, something I can match....by hitting flat.