I have a requirement to send out a custom response to users who upload more than 10 mb file in one of our portal. Default response from f5 just contains the support ID .I couldn't see any option in Response page tab which is specific to file upload options. Appreciate your suggestions.
you are trying to configure a custom response page for a specific type of violation. This can be achieved with iRules. While I don't have a "ready" solution for you, I can share you the link to the manual chapter: Working with Violations
There are a couple if iRule code samples which you can use to make your own iRule. Closest to your requirement is the code snippet that starts with this line #RequestBlockingWithBRP, look at the part below New style Start.
You could also redirect to a custom blocking page, use inline html or iFile. In case you use inline HTML I'd recommend to store CSS/JS/other files in a CDN.