stock calculation of assembly items

To know stock qty of assembly items is required during creation of invoice but unfortunately no stock maintained at present. It will be better if I can know the maximum assembly created with present stock.Either it will calculated at the time of invoice or assembly items stock will be maintained as per choice. when i choose assemble then stock of assembly qty increased and stock qty of bom items will get decresed. when i choose disassemble then stock of assembly qty decreased and stock qty of bom items will get incresed.
I will hope this functionality will be useful.
Thanking you.