Hi @Sujith Mathew Yes! Technically you could create your own Developer portal using .Net or Java or any other CMS technology and use Apigee management APIs. However I will be curious to know the reason behind building your own (any shortcoming with either the Drupal based portal or the turnkey portal?).
The Developer engagement report use a bunch of Analytics APIs listed here. You could enable Developer Tools on your browser to actually see these API calls.