"Roll you own" seems to be interpreted differently in the comments. Absolutely implement existing ciphers/algorithms like AES/RSA/ECC (and various modes of operation/padding) etc. to get a feeling of how they work, and just don't deploy them in production. You'll definitely get a lot from that. Great way to learn while reading the corresponding papers.

What you probably shouldn't do is try to come up with your own encryption scheme/mode of operation/padding scheme and think you've learned something valuable. By all means, try that as well, but know that you've now entered the really dangerous territory.