I would like to know Is it legal to build same website like amazon or any other website's by copying there features.

Example:

I am planning to use amazon as requirement gathering source for my eCommerce project.

I would go to amazon.com and note down all there features and UI design etc, then I would start building website from scratch using the requirement gathered.

Note:

I will not exactly copy the websites design. But only features like Cash On Delivery, Online Payments, Recently Viewed Products etc.

I would like to know how could one gather requirements without looking at competitors or How to get any idea without searching ?

Didn't all similar websites got the requirement's by looking at competitors ?