It really depends on how you want to set things up. If it is representing an organizational structure, it is fairly typical for people to be unable to promote someone to their own level since this generally doesn't make business sense.
If modeling like assets on the other hand, it generally makes sense for someone to be able to let others use anything they have access to.
It is also possible to make a hybrid of the two approaches in more advanced security models because you can grant people the ability to grant users access to something separate from their ability to access it, but this is more user based security than roles (however you could restrict someone from granting access to a resource to a role despite their access to that resource.)
There isn't a right or wrong answer. Choose whatever best fits your security needs.