Download Build Report Tool FREE Unity. 

Build Report Tool – Trying to reduce your game build to less than 50 MB? Need to see which of your assets are eating up disk space?

This tool provides a nice front-end for Unity’s build info. It shows the assets included when you build and how much storage space each of them take.

DLL List: See exactly what Mono DLLs are getting included in your build and how much space they take.

Unused Assets List: Maybe you have files you don’t use anymore? See what assets are not included in your build with the Unused Assets List!