I think Dorin is right
The smaller room/floor is lowwer. So you can't slect it.
Drag select wall, room/floor, furniture.. which including small room.
Holding keyboard Shift+click the wall and other(not small room) to deselect from selection.
2. The tutorial for posting file trow mediafire.com must be updated...
I am very talkative person but I am not good in English...I am sorry if I made any mistake.. 
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