What is the most extravagant building material in Minecraft? [closed]

In Minecraft, which blocks are the rarest, most expensive to build a house from? In particular, by the following criteria:

• Which are the most labour-intensive and time-consuming per block?
• Which are the rarest per-block?
• Which block is the most dangerous to acquire and build with?

This is not a single block, but if you have too much building material and need inspiration on how to use them up - explore the most inefficient house ever. The house consists of only 200 blocks, but took 1,280 blocks to construct.

The architect went insane, shortly after completing it.

Ice, it can only be formed in a winter biome, must be moulded and cannot be made if there is a roof above it.

I'm leaning towards, for the time consuming side, Diamond Blocks. Nine diamonds per block, and combined with their rarity, you could be mining a very, very long time just to build a wall... Gold blocks might be up there too, but I'm not as sure on that one.