Compare outputs on pull request

[Bill Fassbender]

I'm new to bamboo and want to know if the following is possible, and hopefully find an example.

When a pull request is created in bitbucket, I want bamboo to:

Checkout the source and master branch

Build all projects in both branches (the build part is fine, I have a script that handles it)

Compare the outputs of the branches to see new/missing/changed output files.

As of right now, I've got it to the point where bamboo will pull the master branch and build it whenever there is a changed, but haven't been able to find a way to have it checkout anything else.

Thanks in advance.