bill of material, assemblies

I have a worksheet (Excel 2010) whereby I ask for a quantity of a certain type installation. The answer given by the user then uses that as multiplier of a specific associated assembly.
The assembly then produces bill of material associated with that task and the associated quantities etc.
There are several of these questions that a user will answer and the various assemblies use some of the same parts.
I need to produce a composite bill of material for these materials and there associated total quantities needed.
Vlookup; sum product? I am more of an intermediate excel user so I need help bad...
If it would help I can submit the results of the answers that need to be consolidated...