What is the best way to do a permissions system for a low traffic administration system, PHP preferred, but general suggestion is also valuable.

I have an admin with 5 or 6 user types (admins, users, partners, curators, vendors, etc.) each can have access to different pages as well as different functions within a page. Wondering what best practices might be in designing a methodology for this with least amount of if statements, which is pretty much how I handle it now.