Whenever I'm modding a building a came to the same question: Should I add a base or not? By "base" I mean the ground around the building not the collision box. Default buildings have square or rectangular bases and collisions boxes are also limited to those shapes. Even though models can include non rectangular bases or no collision tags you still have that piece of ground attached to the building and this has some pros and cons: Pros of bases: Easy placement, buildings with collision box and rectangular bases will flat the land when placed. No need of previous terraforming. Aesthetics. Bases make the building look better improving the overall look of it. Also the nightlighs will look more realistic when the light illuminates the ground around the building. Cons of bases: Aesthetics. Buildings with bases are harder to blend with your city's surroundings, plazas won't match the building's ground. If you plop the same building several times, the repetition at street level is more noticeable. Restricted placement. Though they are easier to place, the base limits the placement posibilities. Pros of no bases: Aesthetics. Buildings without base allows you to place them more freely, you can place roads that follow the contour of the building's footprint and the possibility of creating customized bases using plazas, trees and other objects. Non restricted placement. Without a base the building has more potential when it comes to placement, you can place them close to eachother, close or away from the roads. Triangle count: Bases add triangles to the models and take space from texture bitmaps which can be used to add more detail to the building itself. Cons of no bases: Harder placement. Buildings without a base need flat terrain, which may need some extra terraforming work. If the ground is not flat, parts of the building may look like floating in the air. Aesthetics. Nightlights will not look as realistic at ground level because the lights will not illuminate the ground around the building.