I have an e-commence business, and have set up inventory with my estimated cost of final product for each item under inventory setup. I also buy raw materials to make the items and code those to COGS. So am I doubling the costs here? Should I do only one of the above things? Either enter the amount of each final product and not code raw materials to COGS or have the inventory item as zero cost and code raw materials to  COGS? 

I also have a couple products I buy and resell. When I purchase the items, should I enter those as an expense or COGS? And do I add the actual cost to the inventory item?