My Rottweiler likes to roll on my feet!
When I'm sitting in my chair, she will walk up, put her shoulder down and roll upside down right on my feet and legs. Sometimes she goes down so hard it almost knocks the wind out of her. This is not for a belly rub.
When she rolls she tries make her entire body land on me usually ending up on her side she is about ten years old, we have had her about seven years from a rescue.
I know the kind of behavior you're describing, but in each individual dog it could have slightly different meanings.
One of the original Rottweiler's 'jobs' was to herd cattle, and when doing this they would tend to lean against the cows, you can still see this tendency to lean against people's legs etc. in most Rotties today.
It's often a gentle type of dominant/assertive behavior, and can also be interpreted as being possessive. If a dog lies on your feet or leans against you in a way that impedes your movement or they object to you getting up/moving away etc. then it's something you need to deal with and discourage right away.
But, if she simply likes to lean on you and roll over at your feet and then is quite happy, it's not something I'd worry about too much. My older Rottie female does this often, but usually it's because she DOES want a belly rub and she'll lie there forever if you let her. Only you can really tell why your dog is doing this and whether it's something you need to deal with or can let be.
I'm sorry I can't help more, but if there are any other Rottweiler owners out there who have input/tips/suggestions or stories they'd like to share please feel free to jump in by using the 'Comment' feature below.
Best of luck with your Rottie :)