Are there any studies available comparing development effort for the two approaches, using an existing tool vs. writing one's own? It is not obvious to me in h

Are there any studies available comparing development effort for the two approaches, using an existing tool vs. writing one's own? It is not obvious to me in how many percent cases the former is better. I have many a times used an existing tool and after getting the thing to work, have come out with a feeling that it may have been easier to do it myself. I used Flex in a compilers course on Coursera, and getting the lexer to match the specifications took about full two days, which sounded too much for the specifications at hand in the assignment. I have written a CFG parser from scratch in less time (not to say that these two tasks are comparable from development effort point of view).