If I remember right The Roaring Silence is heavier on biographical detail than it is on conceptual or musical analysis.
I second @Jonny Cage’s own writings Silence is a good place to start.
Ha I didn’t write Jonny Cage on purpose, I swear.
A couple other Cage books to check out
MUSICAGE - Joan Retallack - these are in depth interviews at the very end of Cage’s life
For the Birds - Daniel Charles - interviews from late 60s to 70s
The Music of John Cage - James Pritchett - gives a broad view of Cage’s musical output, breaks his work into distinct phases and analyzes key pieces in each period of his career