So you mean this roof?
http://img3.wikia.nocookie.net/_cb20120512172600/mario/images/8/89/Peach’s_Castle-Overview-_Super_Mario_64.png
Can you show me exactly where you got a problem with the topology? I use Blender though, but that shouldn’t be a problem here.
(: Maybe i can help you setting up the roof.
PS: Looking at the picture i posted, i would say you can split the whole castle in some parts. The front with the Peach Symbol is one mesh,
The tower in the Middle is one Mesh and the rest is one.
If you can’t get it done, you could send me the .fbx and i would have a look at the roof.
PSS: Here are some more reference pics, just for me, so can compare it better with your work:
