Some people use old straight chairs and put them together....others might use cinder blocks and boards. If you Google you will find several really nice ideas. Good luck!
A lot of Hometalk members have created a garden bench. Here's a link for you to enjoy. I hope you find one that inspires you to make your own. Wishing you the best.
Here's a good one: https://www.hometalk.com/10039280/diy-rustic-garden-bench-for-around-4