I built a shed out of car batteries. The door was difficult, but works, and the roof required a large number of I-beam support columns spaced at 24". One awesome aspect is that it's way more soundproof than anything I've tried before, so I pretty much live in there now.
Initially it was only one row of batteries, but I found that I needed 3 walls to stagger them correctly so that it could block the EMP from a nearby thermonuclear blast.