You did check to make sure this isn’t already covered by an existing solution?
Unity’s Project Auditor has a build report with sizes. In 6.4 it’s a built-in feature. And there’s plenty of other tools I’ve seen over the years.
It’s definitely not something you can just turn into subscription payments. I mean you can try and the visualization may attract some users but it’s just far too easy to ask AI to give you a post-build script that gets the build folder’s size and stores a history of it.