What should I take after completing Diploma in civil?

You can consider following colleges: College of Engineering Pune Lovely Professional University Hindustan Institute of Engineering Technology Chennai, Vellore Institute of Technology P. S. G. College of Technology Coimbatore Madras Institute of Technology Chennai, SCMS School of Engineering and Tec

Lateral entry into B.Tech second year will be a good option, but if you don't like engineering, then there are other options available for you like AutoCAD and many other short term courses.

You can do B.Tech in same discipline. Scope is wide. You can do it from the best colleges of the India such as DTU, BITS College of Engineering Pune Lovely Professional University Hindustan Institute of Engineering Technology Chennai, Vellore Institute of Technology P. S. G. College of Technology C

B.Tech through lateral entry in civil will be best for you