If you have played too muchi in minecraft likew me you will know what is world edit, in one of my posts I posted a video to take reference to the lines.
World edit is a very nice tool to edit huge structures like towers or smalls too, like your house.
a nice tutorial:
http://www.youtube.com/watch?v=lc42-LvvwbYhe have not installed the mod to see lines between selection, world edit is needed to other cool addon: world guard, you only need to select the area, write a command and this area is protected by you...