Without tampering with the editor, this MOD lets you level the area where you want to put a structure. Simply set them in the area you want to level, then take them out. If you want to level any more, place another one next to the one that is currently there; if you put two together, the subject's overpower will prevent you from doing so.
This mod consists of:
100×100 leveling one time
A single leveling of 10×10
One 5 x 215 x 5 leveling
I'm creating someone else with different proportions, so there will be changes. I'll update the mod as soon as I'm done.

Thanks to Vitturino