Cinder blocks rock! So versitile. We have used a brick and board "entertainment center" for years.
For an orchid environment tho:
:
I've seen some people use those grates that office buildings use on their flourescent light fixtures. They kind of look like the top grid from a humidity tray...only larger and you can trim them to size if desired. I think I saw Ross use some in his orchidarium. It was pretty cool. I'm sure you would also be able to use this material as shelving if it was sitting on your cinder block.