Which course should I pursue after completing Diploma in civil engineering?

Look for a job and you can do some course by correspondence as with diploma your only option is another diploma or job.

Sanjaya, you can go for some graduate degree like B.Sc, BBA, BCA etc. And if B.Tech is not a far fetched dream these days as there are many universities that are offering scholarships as well as education loan assistance to students which has made quality education affordable for all. Check website