I found an elevated place in Minecraft and would like to expand its borders. However it seems I can't add a block adjacent to a surface without being able to see that surface, and on an elevated area this means I'll have to be off of the area in order to accomplish this. Is there a way to create a cantilever-like structure, specifically, a way to extend a 'floating island'?
If you sneak up to the edge - holding down Shift (Source) you will be able turn round and see the outside edge of the block just placed. The added advantage of this mode is that you can't actually fall off the block even though it looks like you aren't standing on anything.
Using this mode you can extend your plateau by as much as you like.
It will take a while though.
Tips for building ledges, overhangs, siding, and roofs:
- Crouch – As @ChrisF said, Shift is the default key, which will allow you to examine edges without falling off. If you are at the top of a wall, you are able to build blocks 2-3m down adjacent to the wall. The last block is just barely within reach, and may take some practice to build on correctly.
- Use gravel – Gravel will fall all the way to the ground from wherever you build it, so it is relatively easy to build a nice gravel-tower to wherever you need to do some siding work on a tall or floating building. The advantage is that when you are done you can dig it out from either the top the bottom, and you will gain precious flint from breaking it.
- Use ladders – as you can reach 2-3m below you, you can place enough ladders to have something to hang onto temporarily, there is great risk while hanging on a ladder, as a little slip-up could easily lead to falling to your death
- Use Water + Bucket – This is by far my favorite method for doing touch-up work, or building towers from the top down. Place a water source next to your wall, and jump in. It's not overly difficult to tap/hold space to stay in a reasonable position to build under an overhang. When you're all done, use the water-ladder to get back to the top and remove the source block. Should you accidentally leave the water ladder, aiming back into the waterfall is relatively easy to do before you hit the ground.