Can you place objects on elevated terrain at the beginning of the match?

I'm guessing the answer depends on the definition of "clear terrain".

From the rulebook:
"Objects must be placed in clear terrain outside of any player’s starting area"

From the rulebook glossary:
"CLEAR TERRAIN: Areas of the battlefield where a character can move or make a ranged combat attack without penalty."

My guess is that you CAN place objects on elevated terrain, but the ruling applied at my FLGS was that i could not. This was based on their definition of clear terrain being a square which wasn't hindering, blocking, water, elevated etc. Or in otherwords, a "normal" square.

You were correct and the wrong ruling was made. You can place objects on elevated terrain as it can contain clear terrain.

I was glad to see this ruling. I always place mine on ladders to buildings.