pulse, what a kind soul you are for even considering taking this rottie boy but I agree to wait for a female especially NOT knowing the history of this particular rottie
, what if you find out the hard way that he doesn't get along with other dogs or just some dogs. I'm sure you will be successful in finding a female, just be patient, it will come:) . It's better to have a sure thing then wonder if the rottie could have the potential to turn on your dog, JMO.
Best of luck to you, I'm sure whatever decision you make it will be right for you both.
Judy