Basement issue?

@jenn451 @Pick-a-boo_doo @PugLove888 

This has been going on in the game for a long time.  I think it started about the time the devs gave us the ability to have 4 basement levels instead of the original 2.  @PugLove888 has the right of it though.  Just use the basement elevation arrow and pull down and it fixes it.  It only happens if you have a raised foundation.  It doesn't happen with a flat foundation if you put the basement in before raising the foundation. So, one way to do it is to build with a flat foundation, put the basement in and then raise the foundation.  I don't usually do it that way.  

I do it a little differently than @PugLove888 has shown you.  I always use the basement tools and I build my basements to follow the outline of the first or ground floor so the basement has the same outline.  I also always use the tallest wall height for my basements too, mainly because I want the wall space the higher wall height will give you to put up the collectible space and microscope pictures after I collect them and because I usually put my gardens in the basement.  You have to use the tallest wall height so the trees will fit.  

What I do is this:  I build my house above ground and figure out the floor plan.  Once the floor plan is mostly done and before I do any landscaping, I use the basement room tool to create a small basement room.  Then I drop down and grab the double headed arrow and drag the basement room down.  Then back to the first floor and use the basement wall tool to outline the perimeter.  Once you close the room with that tool, you have a full basement.  Then drop down and select the entire room, go back up with the room selected so you can still see the arrows and the yellow outline.  Then grab the double arrow and drag the basement back up until the ground starts to rise around the foundation, then drag it down one click so that the ground is level.  Then I put in the stairs to the basement and adjust the first floor walls around the stairwell.  As you adjust the basement elevation, there are also some color visual queues to let you know as well.  Green and red.  When it turns red, you're too high.

As you probably already know if you've used the basement room and wall tools, sometimes it won't let you follow the perimeter and turns red.  This is usually because of fences and exterior stairs.  Like you used a fence around a porch and have already placed the porch stairs.  So, any porch fences and porch stairs need to put in last, after you've got the basement in.  And then the landscaping around the foundation.  

This is one of those cases where the order in which you do things matters.  If you do it in the right order, you don't have any where near as many problems as when you don't.  It does take a bit of trial and error to figure it out though.

Hope this helps.