Create a two tall block?

I have a custom block model that is two blocks tall in game and has a GUI bound to it. I used the bounding box feature to set the size and while the outline shows up right in game, the game still thinks its only one block tall sorta. I can't stand in it but I can't open the GUI from the top part or destroy it. I can even place blocks in the top half of it despite it supposedly being solid. Does anyone know how to fix this? 
Also the lighting of the top part gets messed up when its rotated certain ways, it creates a black fade on it and I don't know how to fix that either rip