I think its easy to make the walls on further floors by simply redrawing then on the new floor.

Sweet Home 3D allow you to "align" new walls on floors both above and below by simply using the "alignment vertices" that walls give.

Example:

You draw a room on a house and make a new floor by adding ...

Is there any sci fi theme furniture one can use to design a "space home"?

I am talking about chairs, stairs, elevators, beds, tables, wall/table consoles and etc.