I am currently a sorcerer in the Rise of Tiamat campaign (plenty of dragons to come I assume). I am obviously asking this as a player; I am not a DM and never go through the DMG/Monster Manual (so this could be covered in those books).
Say I cast the wall of stone spell, during or prior to combat against a white dragon, and this wall was designed with arrow slits in it for ranged attacks and cover.
How much cover would we get against the dragon's breath weapon - three-quarters cover or full cover? Or would it work like fireball, which spreads around corners?