Thanks to the internet you will never have a problem finding a Rottweiler breeder; it just may be difficult to find a good one. Patient is key! Never buy a puppy in haste. Take the time to check your breeder out. Sources for your investigation can be local breed clubs, national breed clubs, the AKC, internet forums and dog shows.
Normally a good breeder will interview you very early on. Failing to do this should be an early warning sign. If the breeder does not care enough about where the puppy is going, then he or she probably didn't care too much about the breeding selection. Never buy a dog from a pet shop; you'll be supporting the puppy mills.
A good breeder should ALWAYS make both parents available for your viewing. This is certainly something you should always insist on. At a minimum you should at least see a picture of the father and a pedigree for both parents.
Is the whelping area soiled, moist or dirty? Are there more than a few litters too choose from? Are several adult dogs kept in crates? Are the dogs kept outside or chained? If the answer is yes to any of these questions... take a walk!
If your Rottweiler breeder breeds other large dogs you may want to consider if their interest or attention is devoted to the breed you're there to buy!