I found a whole bunch of pipe with my friends house and he said I could use it. It's probably enough to make a crappy bike. What do I need for framebuilding? How do I know when my frame is strong enough to support a normal persons weight?

Or I was just thinking of making a bicycle "car" thing. 2 seater.

Frames above kid's bikes are made out of good quality aircraft tubing or better. People do make stuff like low riders out of conduit, you might try to find a copy of the Atomic Zombie bicycle builder's Bonanza at your local library or order it off Amazon. Also check out their site. They do a lot of interesting things in marginal quality pipe.

Go here and see if you can't come up with something!

https://bikerodnkustom.homestead.com/