Go to RNG reporter, set the method to Method 5 PIDRNG.
Put the full seed into the "Seed (hex)" box. Add a Synchronize nature if you're using or going to use a Pokemon with the ability Synchronize.
Click generate.
There will be a column labeled "Encounter Slot." There will be a number, that is how you determine which Pokemon will appear.
So go to the top of RNG reporter. Click the "5th Gen Tools" drop down. Click Black or White's Encounter Table. Choose the one that correlates with the game you're abusing on.
Search for Chargestone Cave.
Look for a PID that has Roggenrola's encounter slot, the desired nature, ability, and gender.