Again, maybe try being specific as to your actual needs.  What functionality? What design? 
Every "megamenu" is different based on client requirements.  The mega menues we've done typically have 3 to 4 levels of navigation.  The page type definition has several properties:  
- PageName - system reasons 
- NavName  
- NavUrl  
- NavImageUrl  
- NavTarget
- NavText
Then in your view after you've retreived those items from the content tree (be sure to include node level and node order), you add some logic to get level 1 items, level 2 items, level 3 items, etc.  Additionally add some logic for fields, for example if there's a value in the Image URL field, then place the <img> tag. 
Aside from that, you'll have to provide a lot more details as to what you need from functionality standpoint if you want more details.