[Christien]

Use 2x10, or even 2 2x8s side by side, and add rails to the top layer, so you don't drive it off. If it were me building it, I'd want some way to secure it to the garage floor, to stop it from tipping over. Or secured to each other, or some kind of mechanism to prevent tipping. During my last engine drop, I made platforms out of several small lengths of 2x4 for my jackstands. I had all sorts of problems with them tipping, and had to rebuild them several times before they were sturdy enough to get underneath the car.