Hi Ktynna,
I realise that quite some time has passed since you posted this, but thought I would answer in case anyone else had a similar problem.
I am surprised to be honest that this has been assigned to a BA to do. In reality, it is a Developer requirement and I would have thought they were best to set it up and use it? However, in the name of being a good BA I will give some advice.
As with any other system/Requirement project for a BA, you need to understand who your Stakeholders are and arrange to talk to them. Without knowing the set-up of your company that you work for, I would guess that your best bets are the Head of Development and the Lead Developer (if there is more than one then invite them all to one workshop).
Ask them what they expect to place in their (yes it will be code - but what rules about code will it be?), how people should access the repository and who has access to it.
Then ask them what steps need to happen for each of these. For example, in order to put code into the repository, does that code need to be signed off by anyone?
Next, ask them how they would access it specifically. For example, what search parameters would they use/want? Do they want each piece of code to have a title so that they are easier to find? How long does the code stay in the repository before it is auto-purged? Do they want it auto-purged and if so, what rules do they want you to follow?
They will obviously need some form of UI In order to search for code. I would suggest keeping it simple. Time is short and Devs typically give up if they cant find anything in 30 seconds. The use of Tags might be useful here as well. Maybe the original Code owner, so they could go and speak to them (if they are still with the company)?
Once done, write your BRD or User Stories depending on your methodology used, in the same way as usual. Just because the project is for internal Users doesn't affect how you run it from your perspective.
Then proceed as usual.
I think that covers everything. It does kind of depend on the answers to some of the questions above, but typically I would go with what I have said.