A small one (two levels like you said) is possible, but I think there are better alternatives for a rabbit. The main issue is that rabbits will routinely chew or pull up carpet fibers, or mark soft places like pet beds or hidey houses with soft surfaces. A carpeted cat tree or hut can't really be taken apart to clean.
My husband made a shelf for the xpen to provide vertical space, I call it my "sideways E". I cover it with a blanket so it's soft to jump up on, but the blanket can either be vacuumed off or thrown in the wash. There's a thread about it somewhere here, let me try to find it.
Here ya go... http://www.binkybunny.com/FORUM/tab...aspx
I like the idea of making something yourself (or having something made) because you have control over dimensions and materials.