Reddit reviews How to Read Churches: A Crash Course in Ecclesiastical Architecture

Books,

I have this coffee table book How to Read Churches that is very rudimentary, but also informative.

How to Build a Cathedral is a lot more detailed but also a lot longer.

Kenneth Frampton is one of my personal favorites in terms of modern architectural history.

I would suggest starting out with a book that says a little about a lot, rather than an in-depth book about a particular style or period.