How can an undergraduate civil engineer turn into an architect? What are the pros and cons?

No, an undergraduate civil engineer cannot be an Architect. He will have to go through 5 years of B.Arch degree course again to be an Architect. The Pros would include many, in short An architect would design rather than just execution on site like a civil engineer. Cons in your case would include i

Civil engineering has immense scope in India, and there is a great need for civil engineers in India. However, if your interests lie in architecture, you should definitely pursue your interests. Both are somewhat similar in scope and nature of the job.