I had an idea of implementing clouds as an actual block. As soon as you place it, it begins to float away higher and higher and higher--unless you tie the cloud down with string.

Not sure how they could be crafted...but maybe if you include a bucket of water it would become a rain cloud that you could tie onto a friend's house and make it rain.

A blaze rod or other item cold create a cloud that emits lightning.

Adding snow when crafting would make a snow cloud. Duh!

And then maybe you could make cloud boots that allow you to walk on clouds (without them you would fall through!)

Let me know what you think!