I try to do this at my houses I make for myself, and find using build mode easiest to place some items (like bottles) on shelves. But usually after I leave and come back, I found that the item has sunk down into the table or shelf. It seems picking up the shelf and then cancelling in build mode pulls the bottle I sat on it back up on top, but that's annoying every time. Is there a way anyone knows to keep stuff from sinking down into surfaces? I'd really love to display my model collection, but they all keep disappearing down inside my dresser :S