V1.3.9h
I am a new admin to zen and a bit confused on how to do a custom shipping module. I a very expereienced with PHP and can easily custom code this but I want to be sure
A. Hasn't been done before and I just need a module
B. If I do have to code it where to properly code it so I can distribute it afterwards

My client has a "white glove" service which they assemble and place the piece of furniture in your house. This is 18% of the value of the item itself, not the order.
I tried using the one time fee and the calculations were never correct, always off but at least $10.
Example: Item A base cost of $199.00
Assembled cost is +$80
White glove service is 18% of the combined two.

Has or can this be done? If not where do I code this in? Thanks in advance.