Basically I'm new in web designing and i have a project that requires to make a wordpress theme. Now the questions is do i have to create a theme from scratch or use the concept of parent and child theme(Using thematic framework) to provide a wordpress theme.

What is the difference between designing and creating a theme from scratch.?

Do most websites or web designers use the concept of parent-child theme and use Thematic Framework in designing their web/theme. I really like to see some examples.

When creating that also means developing and that requires learning PHP.