TS3 Circular Stairway... in fact semi circular but it is the way to make it functional in game.
This tutorial is not very difficult but need some ConstrainFloorElevation cheat experience.
First build a 4*3 room on the 5(max) storey (4 on a basement)
On a remainig free tile make a 1*1 tube on the 5 levels (not mandatory but useful to follow these explanations) it will be the center of your staircase. Entrance will face one of the 2 remaining free tile.
Facing the nearest corner from the future entrance dig a 3 modular stairs hole, 2 stairs facing the opposite corner and one stair on the last one. You can do it clockwise or not, no mater.
Delete the stairs (I let them for the pics) and erect at the bottom of each holes a one wall scaffolding. In the 3 stairs hole build it as many walls as you want usable storeys, (adding a tile each level is useful but not mandatory)
You can build a complete backup scaffolding at ground level (may be useful).
Tile each level except 3 tiles along the center on narrowest sides
From the first level of each scaffolding flatten 1 tile wide to the corner of the central tube.
Place 3 stairs each storey threw the holes.
TS3 stairs need 2 flat tiles on foot to be raised and cannot be one above the other if they connect two levels to be usable. (It is possible to place them but they are unusable by sims)
CFE is always false
From the top of your stairway
- delete a center tile along a wall
- level bellow flatten the same tile FROM ENTRANCE SIDE
- back to level, from scaffoldings flatten warped landing.
- place the stairs
- bellow, flaten landing
- Do the same deleting tile along the other wall
...it is the main trick.
continue till ground level, (need not to be flattenned)
From the top flatten the roof.
That's all !
You can delete (or paint) default stair walls and above stairs tiles
Each flat level may be connected to a storey.
You can install doors where you have no landings without cheat, elsewhere you can do it with moveobjects on (they are functionnal). Windowing is possible on each flat tile
Due to the warped walls use a monocolor wall paint is better
Of course you can do it to the top of the tower.
* Rar file is the downloadable PDF version
(possible in french if requested)