Hi,
To design the best model for your application I need to know what stage the project is on now. In other words, what amount of data you process, what most frequent data access patterns are, or maybe you already tried models like an adjacency list, etc.
I have modeled hierarchies of product categories for e-commerce projects and breadcrumb links for CMS and would be happy to work on your project.
I look forward to hearing from you,
Andriy