ravenfalls wrote:can anyone point me in the direction of rules around the interaction of vehicles and buildings/terrain.
to what i can tell, the old rules of no tanks on the roof is gone.
Buildings (as in, Fortifications with actual characteristics, like an Imperial Bastion), are treated as normal units, "and unless otherwise noted is either a friendly unit or an enemy unit (meaning that models cannot be moved across them, but they can be chosen as the target of an attack)", which means by default you can't put models on top of them any more than you could place a Tactical Marine on top of a Rhino. Some rules can override this and allow models to be put on top of them or move across them but they are few and far between.
Terrain (which includes Fortifications that turn into terrain, like the Mek's Workshop or Battle Sanctum), are treated as, well, Terrain. The rules for Terrain Categories permit any unit to move across or on top of Hills, Obstacles, and Area Terrain (insomuch as they don't prohibit it).
Thus, if it's actually Terrain and not a Building, you can place any and all models on top of them, unless a rule says otherwise.
However, if you want to prevent Land Raiders from scaling up walls, you need to give the terrain feature the "Scaleable" feature, which only permits "INFANTRY, BEASTS and SWARM models, and models that can FLY" to be "set up or end a move on top of an Obstacles terrain feature with this trait", while only those same models "can be set up or end a move on the upper floors of an Area Terrain feature with this trait."
So, just make sure to set terrain you want to keep tanks off the roof of as either Obstacles or Area Terrain, give them the Scaleable trait, and don't make them Hills.