I am currently finishing in November with my Bachelor Degree in Building Science (Project Management and Sustainable Systems) I am sitting on a B+/A- average (7.5 gpa).
and am considering doing post-graduate studies in either Integrated Building Systems at ETH Zurich and Building Science and Technology at TU Wien. I am currently applying for internships and graduate programmes at companies however, I would like to know if I have any good chance in getting into those universities so I do not sign a contract worth more than a few months.

I was wondering what would be considered a successful application to either university? Currently I understand that I need to sit a GRE test and good grades are important (but what is considered a good grade? Would I still be able to get in if my gpa drops?). Should I get work experience first such as graduate jobs? The problem with this is that most of my graduate jobs will be Project Management roles whereas I want to study masters in Sustainable Systems (does that matter?). What else should I have to make my application successful?

Any advice/help would be greatly appreciated! Thank you!