I would get the planks built for just this situation. Some cedar like the 4x8's might have a slight sealant on them so that the full effect of the aroma might be consealed.
I would not think that you would need to do the ceiling and back of door if you do not want to, but that would give the full effect. My wife hangs a few clothes on just the cedar coat hangers and the smell is all over out closet from just that. I do like it.
Its just how energetic you are and what your budget is. Now, another thing that I keep eluding to is: when you go to sell this, how will the prospective buyer feel when he/she see's that the ceiling and door is NOT covered?