When building houses, I like starting out with a flat lot. So the “Flatten Lot” tool is very useful. But if there are butterflies on the lot, that section of land will not flatten out. I think it was a 9×9 square that ended up lower than the rest of the lot. When I tried creating the main room of the house, it would not build over the uneven, sloped area. I tried using the ‘move_objects on’ cheat to move the butterflies out of the way, but couldn’t seem to grab them. What I did was just make a narrower house next to the butterflies and waited until they disappeared, then flattened the area where they were. Luckily I have a big enough house that I won’t have to add on to it. I believe another option is to make your Sim catch the butterflies before you start building. Either have your sim catch them before you flatten the lot, or make some stairs so they can reach them. On lots that are pretty uneven to begin with, it may be difficult for your Sim to reach the butterflies. Good luck!