I agree that genetics plays a huge part. One thing I will tell you is how to tell when they are done growing. When you look at the knees at the growth plates you will see a knubby kneed puppy, as it smooths out this is when you know the dog is done growing, if that makes sense.

From my last litter I have a very standard bitch 25 in tall and a little on the finer boned side. She was bred to a beautiful within standard male nice bone and substance. Out of this litter we had 4 males 3 females. All of the males ended up on the smaller side as the bitch, while the females ended up large like the males should have been. Now I'm not saying they were 25 in as there mother but on the smaller side of the standard while my female puppies were on the upward side of the standard. The bitch I kept from the litter is just under 27in tall, she will be bred to a very standard male this August. So the bottom line is really you never know what you will be getting. Mind you if you look at the pedigree of my dogs these are all very well known lines that have been shown from the start. So we are not talking about breeding unknowns. The growth plates will tell you when they are done growing in height though. They will still mature and put on muscle and such after the growth plates close. Some lines will take up to 3 years to fully mature.

Hope that helps a little.