4 Buckets of water
Pick (if you will be digging in stone)
1: Dig out the border of a 4x4 hole.
2: Raise the 2x2 platform in the center to the height you want.
3: Place the 4 buckets of water on the 2x2 platform, one on each corner.
4: Remove the build up on the 2x2 platform, leaving the original platform with trench.
5: Edge the trench in the building material of your house, or, if the resources are available, glowstone and stone half blocks look very pleasing.
6 (Optional): Edit the design to suit your own purposes