I know CSE exist but it don't accept queries like, site:.org inurl:forum which I am looking to use. Can anyone guide me how to built a google powered search engine which can only search in .org domains ?
Google CSE is now known as Google Site Search [google.com]. They let you limit searches to individual pages, entire sites, parts of sites, or entire domains. You can search a number of sites and you're not just limited to one.