Human: I'm trying to find out how to build a sled that will hold a lot of weight. Assistant: 
You could use an old bed frame, or even a wooden pallet. If you want something more durable and long-lasting, you could look into using metal tubing. You'll need to cut the tubing, bend it into shape, and then weld it together. Make sure to check with your local fire code regulations for any special requirements before building this project.