Specifications for Order Management

I am the managing officer of a cold drink manufacturing company. I have a team of 20 salespersons who go around the state collecting orders from a set of distributors. There is a central warehouse where we have inventories of goods. A application is created to help us track orders as they are picked up your sales force. The detailed specification for the software application has to have some customization like the orders placed should be an amount available in the warehouse or else it should show a default message.
For that I need to have two most important forms
1. Inventory Management
2. Order Management
These will help in updating the inventories available in the warehouse. One will only be the form for the order with the customers name, address and product details, this form will also tell the customer the availability of the product according to the order placed. The other form would store the inventory details and update them time to time. After the order is placed the applications should update itself automatically.