Dear Alikhan D,
You can exclude the materials which you want to plan separately by selecting Storage location MRP indicator as 2 -> Storage location planned separately in MRP 4 view of the material for plant and storage location.
Then that material would not be considered in normal MRP.
By planning storage location stock separately:
If storage location stock is planned separately, the storage location is replenished with goods if the stock falls below the reorder point.
Now question of replenishment, in case you want the planned orders to be generated periodically you can go for period based lot sizing procedure with a planning calendar. By doing this procurement proposals will be created according to the periods defined in the planning calendar.
I hope this helps, or at least guides you in the right direction.
Note: The group of materials you want to plan separately must be then at a particular separate storage location in SAP.
Best Regards,
Ameya B.