Buildhelper is a fantastic way to edit and manipulate the world around you. You can quickly build walls with the swipe of a wand or fill and empty large bodies of water. If you want to build a wall out of any type of block, just craft a Gap Filler Wand and select the block you want with it as well as two coordinates in the shape of a wall and voila! It could also be a giant cube depending on where you place the second coordinate.

If you want to add water to fill any air gaps, just use a Water in Gaps wand and fill within the selected coordinates.

Conversely you can remove all of that water with the Remove Water wand.

You can clear big sections areas with the Air Wand.

Or you can use the Cube Digger Wand to clear out a 3x3x3 area in one click. The Digger wand also makes it easy to clear massive structures or mountains.

There are many other wands contained in this mod so give it a try and check out all it has to offer!