I bought a home from the mayor of Diamond City, and the work bench won’t let me build generators but it’s saying I need one, it’s not that I don’t have the materials, the option will not show up?
As per your comment, you are trying to build a power generator at Home Plate in Diamond City.
Home Plate comes with pre-installed power. If you look towards the left side entrance, you should see a fuse box. Just make sure it is turned on.
The fuse box has a standard range. So for lights that are further than the fuse box range You will also require power conduits.