Workset hierarchy and roles

I've done lots of research and tried many things on this forum and can not seem to figure out how to do the following and thus I'm asking the question;

1) I want to have one top level workset on my portal called SALES. All sales people can access this workset.

2) Upon clicking on sales workset a user has two more options; FOODSERVICE SALES and RETAIL SALES. I only want some sales people to see Foodservice and others to see Retail.

3) Within retail sales there are many iviews I want the retail sales people to see. Within foodservice sales there are many other iviews I want them to see. iviews in retail will be different than those in foodservice.

Ok so it seems like a pretty simple drilldown hierarchy to me but I can't get this to work. First I created three worksets.... one called SALES which contains two more worksets; one for RETAIL and one for FOODSERVICE... I then created 3 roles for Sales, Retail and Foodservice. The problem is that anybody with the sales role can then see all of retail and foodservice regardless of wether they have the Retail or Foodservice roles!

How can I REFINE roles in this hierarcial type of way so that all of our Sales users have lots of pretty top level content and can drill down into their respective areas?

Thanks for any help!