Inexpensive Dog sweaters
He has a fur coat. He is built for cold weather. Why on earth would you make him suffer and overheat in cold weather (It would be hard on him going from indoor to outdoor, and his body might not adjust properly and he can get sick/ die)
Animals are not like people as they can adjust their bodies to tempertures as quickly as humans can; they need to do it naturally.
I have about 10 beagles and I live in Illinois, and they all stay in the kennel outside, and they do fine every year, and they a shorter haired, less stocky dog.
whats its for . is it for a bit of fun , special occasion or to go walkies on a daily basis?
If its for fun ( and boy they do look funny in them when there big dogs) ;P cheapest Solution I would say is to either get a cheap human item of clothing for bargain shop or second hand. ma bey a bit of trimmings, ribbon?? sequins ??lol! or even a t shirt print
then you can adapt the clothing/t-shirt to what ever your hearts desireI dont know what your sewing skills are like but Ive put a link to a realizable free pattern for you

now if its for walkies and sensible style then, I cant think its to keep the dog warm being a gsd,
tiffany blue nikes, so maybe dry ?? what about a compromise buy buying a dog rucksack? keeps them covered and serves a healthy purpose !!! as you have a gsd a working type of dog then its the ideal breed to use one with !!
They are useful (for dog as well as you ) the dog wears them like a coat and they have like pockets either side like a donkey , but you cn either put there bits like treats , poo bags etc.