Thank you so much for the clear explanation, all working fine now!
To answer your question, its an existing building, each floor is slightly different, so I need a different space for each space (literally). I am interested though in whether in general the Space Tool is best used in design layer or not - I'm assuming it makes more sense in 3D to have it in design? I am aware I am using it as a glorified annotation tool at the moment!
Best
Sarah