Manufacturing planning appears to be a bit of a black art.  The art is called "

Manufacturing resource planning" (see wikipedia http://en.wikipedia.org/wiki/Manufacturing_resource_planning), and all business processes are considered.  Unfortunately, in the picture on the wikipedia page (http://en.wikipedia.org/wiki/File:MRP2.jpg), budgets and projected sales are indicated in the flow, but these are just the values we need to project.  So, for instance, the budget for a manufacturing project starts with fixed costs such as building construction or rent, and then labor and raw materials must be considered.  All these will vary with projected sales over short run of the construction phase, and of course, the real sales over the long run.  More can be learned about this topic from producer theory in microeconomics, or from operations research, which is more mathematical and computer based.  Of course, the operations research/computational modeling approach deals with optimization of profit in a mathematical space consisting of capital investment, projected sales, etc.

The German translation of the wikipedia "integer linear optimization" planning lists production planning as an application of this theory.  An edited version of the  wikipedia at http://de.wikipedia.org/wiki/Ganzzahlige_lineare_Optimierung is quoted with editing, below:

Production Planning 

Production planning often involves the problem of determining production quantities for multiple products that share common resources (machines, labor, storage capacity, ...). For example, the optimization target is to maximize total contribution margin, without exceeding the available resources. In some cases this can be expressed using a linear program.

The entry goes on to say that "often the variables must be integers, for practical reasons."