I need to provide a quote to an external client for some software. I'm looking to use agile just for initial requirements building (which I'm experienced in from a developer perspective) but I need to do everything this is just a one man job. The client are having a hard time working out what there requirements are and the value I can add will be to sit down with them and work out what they want using user stories etc, I basically need to be a BA for a little bit.

I am looking for good overview of the procedures to go through in the agile process for building requirements, and the continuing process a bit for further down the line. For example the initial inception through to elaboration of epics and building user stories (or not) just need to read a bit about it before the meeting so I know the best way to proceed if I spend a day with them. Having additional resources to provide to the client so that we are all on the same page would be useful too.