comparative study on cost analysis of traditional construction and sustainable costruction
There is nothing wrong with this approach as long as you narrow the focus somewhat. This topic, as you express it, has certainly been done in a variety of contexts and under various circumstances. Your challenge is to search relevant databases for articles about this subject, and see what has been done already.
Some of the articles you read may even have a "Recommendations" section at the end. If you see an article that is from 2007 or 2008 which recommends furthr research in comparing sustainable vs traditional in a particular context or under particular circumstances, you can cite that rticles recommendation as part of your "significance of this study" section.
If you do enough reading about this subject, you'll see "gaps" in the literature where a space needs to be filled.