I want to build a webapp with meteor that groups users in roles, seperated in different accounts (companies).
user 1 (of role X)
user 2 (of role X)
user 3 (of role Y)
@headkit how are we going to advise you without more information about your needs?
I would suggest that the alanning package is a good start, there is also a meteor app that you can use to administer users and roles that you can use (both will save you a bunch of time).
Rather than write something from scratch, look at the package, and ask whether it could be extended, either as a fork of the original package, or you could submit a PR.