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I've hit a dead end when it comes to doing something putting together my floorplan. I have a curved sidewalk in front and I have no idea how to represent it here in Sweet Home 3D
I found this post that is similar to my issue kind of, but I do not see what or where the "floor tool" is in the application (macOS version)
I've created the (temporary) walls for filling the floor, how do I do it? When I delete the walls, will that take the floor with it?
You're on the right track.
Enclose a space with walls, fill in with a "room" without ceiling. Then delete the walls you don't need. The room will stay.
The "room" tool is to the right of the wall tool
Select the tool, double click inside your walls, right click>modify room> uncheck ceiling as Hans says, you can modify the floor texture while your at it.