People coved the housing corns together (try the search function for more details) but it is basically frowned upon.
As far as decoration, many people like using tree branches to provide sturdy, nice looking climbing. You must treat the wood to make sure it is free of any life (go a search on that....I don't know much).
I am a fan of PVC, it is so versitile. You could make anything you wanted out of it, and it is VERY sturdy. However, just plain PVC was a little slippery and boring. I bought a bunch of a fake plant at Walmart and hot glued it onto the PVC. Not only does it look good now, it provides coverage in the tank (making little snake feel secure), but it gives all sorts of fun ways to climb around and fall off of leaves.
If you got a tall tank, it seems like you could cut shelves of glass or PVC (make sure the exposed edge is NOT sharp), then probably use silicone to secure it into place. I've never tried this, but it seems like it should hold decent weight if done well. If it seems flimsy, make climby things to help suport it (or PVC Columns).