Develop a software to manage stock

We have products that consist of many items . Those items are of a standard nature . Which means we can use some of those items to build model A, and if we want to make model B , we use some of those items that are used in model A and we add other items that we have to make model B,
NOW
When we make item A, we consume certain items , and when we make item B we sometimes encounter the stock problem as the material are already used in model A.
This is creating problems as the stock once any customer purchase is supposedly dynamically changing for all items based on a pre set need for each model ( We have those requirements), but we are currently doing it manual ????
We need a solution for this issue so , whenever sales take place the stock for all items based on th stock is updated automatically