I am new to magento2, i want to create my custom product reviews extension by using the default layout and functionalities of Magento2 built-in product review extension.
I am thinking of creating clone of Magento_Review buit-in extension as my custom productreview extension.
Is this the correct way?
If you're not going to need the original review module and it's close to what you would need, I would keep that one there. Then create a new module Your_Reviews that's dependent on the Mage_Reviews modules and it then modifies the functionality that you don't want.
This can be achieved by injecting your own dependencies in place of core one: http://devdocs.magento.com/guides/v2.2/extension-dev-guide/depend-inj.html or using plugins http://devdocs.magento.com/guides/v2.2/extension-dev-guide/plugins.html or using event observers http://devdocs.magento.com/guides/v2.2/extension-dev-guide/events-and-observers.html.