To answer the original question, do not backfill with gravel. It is cohesionless and will not provide proper resistance to overturning. Since there is drainage on both edges of the footing, the resistance to sliding is provided only by friction with the underlying soil. You mention a roof, but normally a roof would be on the excavated side of a wall. In this situation, rainfall on the backfilled side would run through your gravel, to the footing. If the drain is not sufficient, you could lose sliding resistance due to the new moisture and it could all slide to the excavated side. Drainage behind the wall is very important, but you don't want encourage runoff to pool at the drain.
If the wall was designed and built as a proper cantilever (see the CRSI Design Handbook for examples), then your backfill should be lean clay, clayey sand, silty sand, or a similar material Avoid organics and expansive soils.
It may well be intended as a basement foundation wall, which relies for the floor diaphragm at the top for resistance (carrying the load from one side of the structure to another, rather than resisting the entire soil load as a cantilever (think flag pole.) Backfill partially unless the wall is designed to be a true cantilever. Construct the floor or other diaphragm, then finish backfilling.
