After this diploma you have the option of going for AMIE and if you complete that either full time or part time you will become a full-fledged engineering degree holder.
If you do not want to go for the long AMIE route you can think of short courses in structural designing, building and interior designing, computer-aided designing courses etc. You have to find out exactly which one is of your interest, that is, you have an aptitude for the same.
As you have completed the diploma, I will advise you to join a job, however small, in the industry so that you can gain experience and also pursue short courses part time. Please remember that the real experience is obtained only when you are having a job. After gaining the experience the prospect for switching the jobs or applying for higher jobs increase significantly.
Knowledge is power.