1 and 2 are similar in meaning. Both refer to the habit of reading books. 3 is different. It is referring to something that happens only when you read books. For example, you might start singing loudly while reading. Sentence 2 should be "It is a strange habit of mine reading books"

Due to making the sentence in a different grammar style (using reading instead of read), your 2nd sentence should be: Reading books is a strange habit for me. The meaning of the sentences are the same. 3rd sentence is not possible to say, say either of the first 2 sentences instead. If you want to indicate that you've "a strange habit" when you're reading books, say: When reading books, a strange habit of mine is ....