Answer:
I can be as thin as a picture frame but my insides have many things you can see.
What can be measured but has no length, width or height?
How many bricks does it take to complete a building made of brick?
Casper was a friendly one and Demi Moore made a clay pot with one.
When this is found in a road you are forced to make a decision.
Though not a plant, has leaves. Though not a beast, has spine. Though many wouldn't need this thing, It's more valuable than wine.