Minecraft wiki entry for From_Below_CSG, associated text: Both dirt and cobblestone represent temporary blocks you'll need for assembly, and the smooth stone is (bottom) slabs. (Not all the water will be there until you remove the dirt.) It's best to start by making the pillars and roof, then run a ladder up one of the pillars and work above and below the roof. (The ladder shown is outside, but it doesn't have to be if you put a bit of wall to support it.) Place the water behind the blocks and cover it with the slabs. When everything else is ready, place the lava, then once it has flowed down to the ladders, unblock the water. Last of all, go downstairs and mine the other three temporary blocks. They should be replaced by a gush of water, then new cobblestone. The obsidian is again optional, but helpful: accidentally mining the blocks behind the lava will produce a major mess.