Can you post a picture?
Many Lay people call Modified Bitumen a "rubber" roof.
In the roofing industry, a "rubber" roof is Ethylene Propylene Diene Monomer (EPDM) so we need to know if yours is actually EPDM, or if it is something else.
1. Is it leaking?
2. How many plies thick is it?
3. Does it have any surfacing on it now? (Granules)