When doing social sciences research for a dissertation, it is usually best to use an established theoretical framework. The main reason for this is that it will make your dissertation research more acceptable to the people who will be reading it. In order to succeed, you need to have your dissertation be accepted by your committee. You will likely need to have it impress potential employers. You might need to have it be acceptable to peer reviewers who will determine whether your work will be published in an academic journal. These people are likely to be more receptive to a work that is based on an accepted theoretical framework. A new framework proposed by a nobody graduate student is less likely to be acceptable.
There is, however, one reason why you might want to develop your own framework. If you are able to develop a framework that is really compelling, you will be a much hotter commodity. If you show that level of creativity and insightfulness, you will be more likely to be seen as someone who is going places. If this happens, you will likely be more able to get a good job and to get the publications that you need to eventually get tenure.
In other words, using an established framework is the safe way to go, but making up your own (if you get it right) is more likely to make you a rising star in your field.