The Wood, Metal, and concrete items all snap together interchangeably with no issue. The Barn, warehouse, and scaffolding do not. Some things snap together the first time, and then a second does not snap. Getting a 2 storey barn using high wall with a wood upper floor in between and a concrete roof does not really work correctly, and I can see no resaon it shouldn't. Sepscially if I use a 2 storey metal wall with a wooden upper floor in between and concrete roof I have no issues whatsoever. Also using the scaffolding ladders on anything except scaffolding fails. I think it should work as I can use the barn ladder on a wooden floor, or the concrete ladder on a metal roof. In short all reasonable items should snap together; wall to floor, roof to wall, ladder to roof or floor.