Is there a way to customize the bottom tabview buttons to have different sizes and even shape. Something like this:

Thanks!
If you want the UITabBar to have a different shape or size, unfortunately, you won't be able to change it even by subclassing UITabBar.
To get started, you'll want to take a look at subclassing another type of UIView -- either vanilla UIView or UIImageView, add icons to them, and configure touch events to make them do what you want.
Here's some helpful resources for you to get started: