Is point above some entity?

I want to define whether some point is above some entity (BuildingBlock in my case) or below. I can get position of entity, but where can I find sizes of entity's sides? Or there is easier way for solving it?
[DOUBLEPOST=1455108066][/DOUBLEPOST]I mean, for instance we took foundation. How can I determine, does player stand on it, if we have his coordinates?

 

You cast a ray downwards from the player position and check which entities it hit.
m-Teleportation uses this, see the method PLUGIN:isOnFoundation.

 

That's what I've done. Too bad I forgot to write the idea here. Anyway, thanks