I have never owned a Rottweiler, but here is what I've gleaned from Rottweiler owners. The advice is worth what you paid for it. 
Rottweilers were bred to herd cows. A lot of them herd by leaning on the cow and making the cow move - that's why they're so big and have so much muscle, to be able to move a cow by leaning on its legs and making it step to one side. They are working animals and will need a job to do, whatever that job is. It can be as simple as bringing you the paper or as complex as service dog work, but they need something to do to keep busy or they get bored. A lot of them do lean on people to herd them and get them to do what the dog wants - it's really hilarious to see! And yes, a lot of them do think they're lap dogs, especially the ones who were loved on as puppies.
Because they're big, even if they don't mean to they can do a lot of damage if they do get upset. It's not that a Rottweiler is more dangerous than a Chihuahua, it's that the mass of the Rottie makes its bite or tackle more potentially damaging. After all, you can throw off a Chihuahua if it attacks you, but you can't do the same with a Rottweiler. The solution is to get them obedience classes and keep working at it, and to socialize them constantly. A scared animal is more likely to bite. If you take them out when they're young and get them used to new situations, they're less likely to be scared and react with fear aggression. This is not a breed to skip the obedience classes. This is a breed to teach to love doing what you want and reward with attention and love and pettings when they respond appropriately.
As I said to a friend last night on Facebook when she posted a picture of one of her Rottweilers cuddling with her teenage son: "Rottweilers are so scary! Look at her. She might lick him limb from limb!"
Best of luck in your search!
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