how to make a dog crate two tiered with ramp? best material to use and how?

I don't mean to bombard the forum with loads of threads but I am trying to decide on the best housing lol.

If I kept two bunnies inside and used a large dog crate with a large pen attached, what's the best thing to use to make the crate two tiered with a ramp? And how is this best done?

Thankyou ...

I think there is a short how to in the sticky thread. http://forums.rabbitrehome.org.uk/showthread.php?304613-Indoor-Housing

Basically we put batterns across with screws each end to stop them slipping and made a shelf the same size as the inside of the crate and rested this on the batterns.