Anyone who breeds their bitch is a breeder. That is how one starts out breeding. The preparation prior to breeding that bitch, and the decisions you make in breeding the bitch -- that will determine whether or not you have a leg-up on becoming an excellent breeder, or if you are in danger of becoming part of the problem.
Breeding a standard size GSD bitch, which I take to mean a bitch between 22-24 inches at the whithers, and somewhere in the ball park of sixty some pounds, to a giant shepherd is the question. Frankly, I do not think it will be any more dangerous than breeding the bitch to a standard male. I mean, I have heard of the weirdest hook-ups chi-doberan etc. Obviously if you have a 120 pound male and a 8 pound bitch, that isn't going to work so well. But a 120 pound male can probably breed with a 60 pound female without serious repercussions.
The size of the puppies at birth will be dependent on the number of puppies that are thriving, and the nutrition the bitch is given. Even Leonbergers are approximately a pound or so at birth, so it is conceivable that a litter of Leonberger puppies could be surgically planted inside a GSD and whelping would most likely go off without a hitch. So I in my best opinion, a standard-sized bitch could whelp and raise a litter of puppies out of a giant male without any more trouble than what is possible with any breeding: stuck puppy, pre-mature labor, end of labor with puppies still within (distocia?), eclampsia, dead puppies, dead bitch, and some I simply am not thinking of.
I don't think that the ethical or moral aspects of breeding this combination was asked for. But since the moon is full, I might as well add that opinion as well: why? Why take a bitch who is within the standard and breed her to a dog that is seriously over-sized? If you aim is to produce large dogs, why not start with a large bitch and breed her to a large dog? When you become versed in breeding, you will see that balance is what is needed. If you have a dog who is under-angulated, the proper thing to do is to breed to a dog with correct angulation, not an over-angulated dog. The idea is to produce a dog that best fits the standard. If you are already starting with a bitch who is within size-wise, why would you want to use a large dog? I think you would have a better chance at getting what you want if you start with a bitch and dog that complement one another. If you have a bitch who is far different from the dog, you will probably get puppies that are all over the place, and you will have no way of telling how big they are likely to get.
And the people who might want these puppies will want to know this. I mean, you can show them Fido - 120# and Bella - 60# and say somewhere around that big.
Jenna, RN CGC & Babs, CD RA CGC HIC
Heidi, RA CGC
SG3 Odessa, SchH1, Kkl1, AD
Ninja, RN CGC & Milla, RN CGC
Joy, Star Puppy, RN CGC
Dolly CGC & Bear CGC