Roller's rights is one of the rules of marijuana that stoners abide by, which states, succinctly:
He who rolls the smoke has rights to the first toke.
I've never met any group of dedicated potheads who didn't follow this rule, and the term "roller's rights" tends to get thrown around anytime someone suggests lighting up substance that another person rolled. It is really common for the roller to give up their roller's rights to another person, however, especially if they've already claimed roller's rights on weed that was smoked earlier that day.
The situation is a bit more socially complicated when the marijuana used for rolling was bought or grown by someone other than the roller. Usually roller's rights in that situation are superceded by a stoner's right to smoke their own supply, but I've seen some groups who take rolling very seriously (almost like it's an art form) and will stick to roller's rights even in this case. I'd say it's best to discuss things beforehand to avoid bickering after, but then you run the risk of being a huge buzzkill. Thanks to the relative ease of access to marijuana compared to other drugs, most people are cool about this kind of thing and won't take it very seriously if you commit a social faux pas.