the first thing that pops to mind is to give every tile an instance variable called "level" or something. bottom would be zero, higher blocks would get 1, 2, 3, etc depending on their height.
Als your player collides with a tile, keep track of the current level as an instance variable of the player, and whenever you collide with a tile with a different level as the player has at that time, and the tile is lower, then subtract them to know how many levels he dropped
just a suggestion, maybe there are faster ways
greets