Leveling Terrain in The Sims 3 (Xbox 360): Workarounds Only
The Xbox 360 version of The Sims 3lacks the terrain editing tools (Raise/Lower/Level/Flatten) present in the PC version. You cannot precisely level a lot.
Workarounds
Choose a Flat Lot: Start on the flattest available lot in Edit Town.
Foundation/Deck Trick: Place a large foundation or deck covering the build area; it creates a level platform. Build on top. Delete foundation later if needed (floor stays).
Terrain Paint "Smoothing": The landscaping tool's "Smooth" brush slightly evens small bumps — useful for cosmetic blending, not structural leveling.
Basement/Foundation Height: Adjust foundation height before building to match sloped terrain at one corner.
For true terrain control, the PC version (with mods like NRaas) is required.