When you want to express the idea of enhancing or expanding on an existing concept, the phrase "build upon" is a useful way to convey your message. However, there are several other synonyms you can use to add variety to your language and express your ideas more precisely. Examples of synonyms for "build upon" include "develop", "expand", "elaborate", "advance", "augment", "enlarge", and "improve". Each word carries a slightly different connotation, so choosing the right synonym depends on the context in which it is used. Mixing and matching these synonyms can help you to convey your ideas more effectively and keep your writing dynamic and interesting.