Custom Left Vertical Admin Menu Items

Hi Guys

My Idea is to totally customize the backend of my wordpress multisite,as it will be a backend membership site software. The last step I am stuck is to completely customize the left vertical menu bar, by creating my own topics and then adding some of the top menu items to these topics as sub menu. Also if the top menu already has sub menu items, these items will just be sub menu items of the sub menu. I will use OZH Drop Down Menu to make it a horizontal menu, so the sub sub menu items will look really good then.

Hope someone know how to manipulate the function.php to do the above

thank you so much in advance