Space saving items- toilet/sink combos, corner sinks/toilets, etc

I’d like to use the space under the stairs. I tried to place a door and a desk the other day thinking I could make a small study there and was sad to gong out sims can’t get In.
A shelving system under the stairs would be nice too.

Another thing I want and I made a thread about it, is being able to use the space under a roof to make an attic or extra rooms.