M.Tech

M.Tech in structural engineering involves advanced study of the courses components such as structural mechanics, finite element analysis, structural dynamics, structural reliability and optimization, reinforced and pre-stressed concrete, steel structures, design for wind and earthquake, tall buildings and towers, computer applications in structural engineering, etc.
Admission to the course is based on the candidate's performance in the relevant entrance test and subsequent rounds of counselling. The average tuition fee charged for the course in India ranges between INR 2 and 7 lakhs for a span of 2 years and the average annual salary offered to such professionals ranges between INR 2 and 10 lakhs, increasing with experience and expertise.

If you are interested in higher studies or research then you may go for M.Tech. For doing M.Tech, you should have at least 55% in B.Tech/BE and a valid score of GATE. I am enlisting a few good colleges for M.Tech IIT Roorkee, IIT Guwahati, DTU, IIT Varanasi, Anna University, IIT Dhanbad, NIT Surathkal, NIT Tiruchirappalli, NIT Warangal, IIIT Hyderabad, IIEST Howrah, College of Engineering Pune, Jadavpur University, IIIT Allahabad, NIT Calicut, Birla Institute of Technology and Science, Lovely Professional University, Jalandhar, Punjab, College of Engineering, Anna University, Chennai, Delhi Technological University, Delhi, Indian Institute of Engineering Science and Technology, Ramaiah Institute of Technology, Bangalore, VIT Vellore, Jadavpur University.
If you are not interested in learning technology any more, only then you should change your field and pursue MBA. You should have cleared any one entrance test (such as CAT/MAT/XAT/NMAT/CMAT/GMAT/NEST) accepted by various colleges and should also have minimum of 45% to 55% in your Bachelors (any stream) for admission in the same. Admission in MBA is done via two modes- either through an entrance exam or direct admission which is based on merit basis or management quota basis. The top schools of India mostly use some entrance tests score to provide admission. MBA graduates can enjoy better career options. Some of them include Finance, Marketing, Operations, Human Resource, International Business, and IT. There are several popular job roles available for MBA graduates such as Business Manager, Human Resource Specialist, Accounts Executive, and Public Relations Specialists. You can do MBA in any specializations of your interest. Some Good Colleges that can be considered are:
NMMIS Mumbai
XLRI- Jamshedpur
Goa Institute of Management -Goa
Lovely Professional University-Punjab
K. J. Somaiya Institute of Management Studies and Research - Mumbai
School of Management, D. Y. Patil University - Navi Mumbai
Maharashtra Institute of Technology Kothrud -Pune
International Management Institute - New Delhi
Management Development Institute - Gurgaon
Christ University - Bangalore

Civil is more of a core branch while design is not. It completely depends on your interests as to decide where you should go. Institutes do matter but branch matters a lot more.
Quality of teaching: I can tell you that civil department professors at IIT-Bhubaneswar are quite good. Although I don't know much about the professors at IIT-Guwahati but still, IIT-Guwahati being older will be equally good if not better.
Campus life: IIT-Guwahati has a much better campus life than IIT-Bhubaneswar, so there will be much better exposure. But newer IITs are improving at a fast rate. There will be fewer students in IIT-Bhubaneswar compared to IIT-Guwahati so there are better opportunities for an individual to actively participate in extra academics activities like societies and fests. Although sports facilities at IIT Guwahati are much better than IIT-Bhubaneswar.
Placements: IIT-Guwahati design will be mostly offering non-core placements while at IIT-Bhubaneswar you have a much better chance to get core placements (this year more than 70 percent students got core placements). So, if you have more interest in the technical stuff then I would suggest IIT-Bhubaneswar civil as a better choice over IIT-Guwahati design. The average package for IIT-Guwahati design will be greater than IIT-Bhubaneswar's civil branch.