Short answer, yes
I cant provide you the complete long answer, but to help you along the way:
- You need to provide the foundations within your graphics.
- Depending on what you want, you may need to use flag OBJ_FLAG_NO_FOUNDATIONS
For example, you may want a house on a slope with pylons as foundations (so that you still can see the slope underneath), for that you need the flag so that the game-foundations are invisible.
EDIT: I am not too sure about this though...
-Now comes the tricky part...
You need to make your object slope-aware, so that they can only be built on the slopes (or also the flat tile) that you provide graphics for.
With this I cant help you, but it is achievable.
You may know the ingame-warning something like: OBJECT CANT BE BUILT ON THIS SLOPE, thats this thing
Sorry I cant be of more help, but at least you know that it can be done