Usually there are suppliers, customers and users in an inventory management system.
Suppliers
Supply raw materials (cash or credit)
Receive payments
Accept returns (If their materials are not up to the expected quality criteria)
Customers
Place orders
Purchase finished goods (cash or credits)
Make payments
Return defect goods
Users
Check quality of raw materials
Return defects to suppliers
Accept returns from customers
Make payments to suppliers
Receive payments from customers
Maintain stocks
Transfer stocks (if the company has more than one branch)
Track debtors and creditors
P:S - machan are you going to develop an inventory management system ?