Adapting the 'Posts' menu

Hi,

I’m creating a WordPress plugin.
I want the plugin to have a ‘Products’ menu in the WordPress back-end (admin) section where you can view/add/edit/delete products.
The pages to manage these products should be nearly the same was those of the standard WordPress ‘Posts’ (where you can manage your posts).

Here comes my question:
Can I just copy the existing php files that make up the ‘Posts’ menu and modify them? Or is this bad practice?
Or would it be better to just start from scratch?

Thanks!