Hi J Gill,
you requirement can of course be addressed by a custom development. However it is difficult and needs expert coding skills with characteristic dependent planning CDP in APO.
I would recommend to use PDS because it is the new default master data for APO.
Similar requirements are addressed by
Long
Products Planning
Pasted from <http://help.sap.com/saphelp_SCM700_ehp02/helpdata/en/7b/8a7d360998de4a8ff927215ebfd702/frameset.htm>
They have Length-Based Net Requirements Calculation.
In that specific net requirement calculation there is also a sequence of choosing the charactistic values of receipts.
You can see there how that could be done.
However that is very demanding to adapt this to your needs.
But it can be done.
I would do it the following way.
After you decided for the resource you can run a heuristic for the roll component for example
SAP_PP_003 Planning of Shortage Quantities /SAPAPO/HEU_PLAN_DEFICITS with standard netting.
Function module /SAPAPO/RRP_NETTING
Use BADI Definition Name /SAPAPO/RRP_PLANNING
method AFTER_NETTING
let the standard netting work without restriction that means characteristic requirements with a wide intervall for all possible widths.
then read the order and the resource in the BADI method.
the method should deliver a list of possible receipts.
You can then sort the list and assing the suitable receipt to the input node of the order.
If you want to keep the relationship, fix the pegging.
That is just a real quick shot which needs a lot more evaluation and testing but for the start it might be the right hint.
BR and good luck
Frank