We made one from an old door. It was just a plain solid core door. Had hubby put 4 large eye hooks in each corner and attached it to a strong beam on porch. I made a large mattress by covering foam.
Here's a tutorial: https://www.youtube.com/watch?v=4NVMr3RmBh4
Awesome tutorial https://www.hometalk.com/17540877/diy-pallet-swing-bed