It doesn't sound natural, but I understand what you're trying to say. Maybe, "After hearing the lengths you went to, I began to see you as a maniac." Anecdotally, I think in this situation you should change "length" to "lengths" and "through" to "to". I don't think there's any particularly good reason for this, it just sounds more natural. As for adding "After" to the beginning, it's totally up to you, but it sounds better to me. I'm not a very good writer, so take this with a grain of salt. Additionally, here's the Cambridge english dictionary: https://dictionary.cambridge.org/us/dictionary/english/go-to-great-lengths