The method can be used on a house that is already built with a foundation.
Remove all furniture, doors, windows and wall decorations from the first floor. You can place them temporarily on the second floor or use MOO to place them in the yard. You can’t have anything on the floors or walls above.
Step 1: Go down to the ground level under the foundation.
Step 2: Use the level tool to level the area.
Step 3: Place stairs going down. Make sure it is just 4 steps.
Step 4: Level an area from the bottom landing from the steps for a couple of tiles.
Step 5: Place a second set of stairs going down. Again make sure it is just 4 steps.
Step 6: Repeat step 4.
Step 7: Repeat step 5.
Step 8: Place a floor tile on the bottom landing of the bottom set of steps. (Ignore the floor tile on the lower left. That is my mouse still holding one.)
Step 9: Hammer the three sets of steps.
Step 10: Level the basement from the floor tile outward. DO NOT go to the edge. Go one tile from the edge of the foundation. There will be a slope.
Step 11: Add walls around the exterior of the defined basement.
Step 12: Go upstairs and hammer a square of foundation in the centre of the area.
Step 13: Go back down to the basement and hammer the foundation until you reach the walls.
It should look like this when you’re done.
Step 14: You can now place your stairs. I used spiral stairs to save on space.
But regular stairs will work too.
This is done by leveling the two circled tiles and removing the foundation. Then add your window. You can do this in multiple areas where it will look nice.
Don’t forget to recolour the sides of the floor tile.
That I hope is clear enough. If you have any questions, please feel free to comment.