If you are going to be doing a lot of work with either curved roofs, complex basements, or split-level homes, then this small and easy hack will make building MUCH easier for you.

It will allow you to build walls on uneven terrain, raise terrain even when there is a wall on it, and much more. (It does this in a different way from the constrainFloorElevation cheat)

If you have not grasped the concepts of advanced building yet, I recommend you do not do this tutorial until you have... otherwise it may in fact make building harder for you.

As always, when editing game files, you should always make a backup of the file you are going to edit, in case you do something wrong.

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First, open up the "My Computer" icon on your desktop and go to:
C:\Program Files\EA Games\The Sims 2\TSData\Res\Catalog\Scripts

In that folder, you will see a file called walls.txt
Open the file with notepad.

Now, click on the Edit menu at the top, and choose Find from the list.
Type in wall 1 and then click Search

It should take you to the part of the file that looks like this:

# normal walls wall 1 defaultPattern "blank" wallThickness standard mayChangeSurface true mayAttachObjects true mayCutAway true requiresFlatBottom true requiresFlatTop true submersible false deleteTool partition thumbnailResource 0 0x499db772 0xe9261348 thumbnailResource 1 0x499db772 0xe9261347 catalogTextIndices 0 1

See those lines I highlighted above?
Change them from:
requiresFlatBottom true
requiresFlatTop true
into:
requiresFlatBottom false
requiresFlatTop false

Save the file, and exit Notepad.

Now you can just open up the game, and play around with changing the terrain near walls :)

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