Unable to build basement on Potters Splay [ Edited ]

[PastelSpoonie]

Product: The Sims 4
Platform:PC
Which language are you playing the game in? English
How often does the bug occur? Rarely (0% - 9%)
What is your current game version number? 1.63.136.1010 (64 bit)
What expansions, game packs, and stuff packs do you have installed? All except Eco Lifestyle
Steps: How can we find the bug ourselves? Build basement on Potters Splay
What happens when the bug occurs? unable to due to being "outside of lot"
What do you expect to see? being able to build basement
Have you installed any customization with the game, e.g. Custom Content or Mods? Not now. I've removed them.
Did this issue appear after a specific patch or change you made to your system? Yes
Please describe the patch or change you made. Haven't played since before the pre-Eco Lifestyle patch so unsure of which one broke it. Restarted game and it fixed itself.

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Basement Tool Glitch 

Error when trying to build 

[CGrant56]

@PastelSpoonie 

Ok, judging from your pictures, you're trying to use the basement tools while building on a basement level.  While you would think that should work, those tools don't work that way.  To use those tools, they are used on the floor above, not on the basement level.  What those tools do is allow you to trace the outline of the floor above so you can get the same footprint on the basement level.  You need to use the regular wall tools if building on the basement level itself.

Hope this helps.

[EuphorialQueen]

@PastelSpoonie 
@CGrant56  makes a valid point.
"To use those tools, they are used on the floor above, not on the basement level."
This is correct for that particular tool. I also noticed there are no grid lines in your pictures.
Use the "G" on the keyboard to turn grid lines off and on.
With grid lines on you should be able to use the wall tools to build a room on any basement level.