Can flying units that are inside a building move through walls?

So i was playing with my friend the other day and something interesting came up:
I had my venom hidden inside a ruins building and during my movement phase my friend asked how i can move through the wall... Flying lets you ignore vertical terrain but what happens if you are already inside a building because the rules state that only infantry can breach walls.
Does that mean that i can fly above a building but i cannot stop inside because a vehicle can not breach walls?
Anyone know the rules that are going into effect in that situation..?

Interesting question. I would argue that when I fly my Venom over an obstacle after hiding behind it and then charge at an enemy on the ground, I am 5 feet in the air most of the time, boosting to 10 feet when I cross it, even though my GW model doesn't look that tall.
As such it doesn't impede me.

The same would apply from a ruined wall. I think I'd allow the clear move.

Now, what if my Venom is under a ruined ceiling...?

Its generally played that a Fly model (like our Raiders and Venoms) can move over models and terrain in the movement phase without penalty. Meaning it can hop walls (in the movement phase).

Something to keep in mind is that Fly does NOT work during the Charge and Consolidate/Pile In phases. So your Reavers CAN move+advance over the wall, but CANNOT charge/consolidate thru the same wall. But they CAN charge/consolidate over enemy models.

What fisheyes said.
When a unit with fly moves, you ignore all vertical movement, so even if you would have to ascend 20" just to get over the wall, it doesn't count against the unit's move.

What if there is a floor above you. Do you have to back up to clear the floor or just go vertical strait up thru the floor.

The rule says you can only move thru enemy models in the Charge/Consolidate/Pile In moves. If you physically cannot go thru the floor, you got to go around.

Same for Monsters/Vehicles/etc

Infantry ignore the restriction on terrain with the Breachable keyword. Otherwise they too would need to go around.

EDIT: However, you could punch thru the floor if you are directly below within 5" vertically of the opposing unit.

So you cannot walk thru the wall, but you can punch thru it, like Jack from the Shining.

"Here's Reavers!!!" XD