The Bone Builder is a feature in UMA 2.7 that allows you to pre-create the bones on an UMA character at edit time so that it is easier to use with other Unity components, for example, character controllers. Once you supply a Dynamic character avatar or a gameObject and an uma text recipe, you press "Generate Bones" and the bone hierarchy and mecanim avatar will be created for you.
The Bone Builder is found by going to the toolbar -> UMA -> Bone Builder.
Bone Builder Window
If you use a Dynamic character avatar the list of bones will be created from the race you have chosen on the Dynamic character avatar. Once you generate the bones you will not want to switch to another race with a different skeleton without first removing the generated ones and re-running the bone builder.
You can also use any GameObject, in which case the bone builder window will expand to require a "Base Recipe" which is an UMA Text recipe asset. The bone objects will be created from the list found in that recipe.
Remove UMAData: An UMAData component is added to process the base recipe and generate the bones but usually is not needed during edit time. Keeping this checked will clean it up automatically, but in case the user wants to keep the component around they can uncheck this option.