Refined Bamboo Blocks are a type of block in Portal Knight, and are even used for a quest during the Spring Event. In order to craft this block you will need to get a workbench. The level of it does not matter, since the Refined Bamboo Blocks can be made at level 1.
Each Refined Bamboo Block cost 1x Bamboo Log to create, so you will need to farm a lot of bamboo if you are going to be making an entire house from Refined Bamboo Blocks.
Anyway, just use the workbench to craft them, and pick them up when they are ready.