Please pull out any keywords directly from your thesis that you think are most important to describe your work. These words can be put into the library catalog and the institutional repository and will be fully searchable.
If you are stuck for ideas for keywords you can look at the Getty Art & Architecture Thesaurus or the Library of Congress classification. However, you should always be comfortable just selecting terms from your own text. Do not worry about finding the "right" term -- any words you choose will be appropriate.