Manufacturing as third party

First identify what kind of costing is used during manufacturing process. For example, if you use absorption  costing, all overheads will be absorbed into the cost of unit. The disadvantage here is, if other batches and orders are manufactured perpendicularly, then the costing is not accurate as other products costs will be allocated to this product. So, keep track of batch costing and add a markup for profits. I believe you must be like a wholesaler distributing finished goods to retailers and hence profit margins vary as yours will be lower than the actual selling price.

Next, the ledger accounts needed for production and sales are:

Debtors

Creditors 

Inventory

Purchases

Sales

Fixed overheads

Variable overheads

When they have paid for it, COGS, the purchases, closing and opening inventory, direct material entries will be zero. The rest is the same, account for expenses and overhead costs. Eg

Add: Direct Materials Used

Add: Direct Labor Used

Add: Manufacturing Overhead

Add: Beginning Work in Process (WIP) Inventory

Deduct: Ending Work in Process (WIP) Inventory

= COGM

Add this to COGS along with depreciation. It should work out.