MasterPage and Contentpage Query

Dear Gurus and Experts,
I am designing a Masterpage (Comms.master) with 3 different contentplaceholders namely:
1.  MainMenuContent - a page contains main menu. located at the top of the screen. default page is ("mainmenu.aspx")
2.  SideMenuContent - a page contains menu from the selected main menu. located at the left side of the screen, below main menu. default page is ("sidemenu.aspx")
3.  DetailsContent - a page displays the detail of the selected side menu. located at the center of the page. default page is ("details.aspx")
here is my data:
Department 
      - Department Message ("department.aspx")
      - Organizational Chart ('organizational.aspx")
Products
      - Books ("books.aspx")
      - Watches ("watches.aspx")
      - Acc ...