I had a room in my basement that was under the concrete stoop in front of my home. I removed the doorway and tied in to the cinder block foundation wall. I knocked the stoop down to grade. I am left with an empty 6' cinder block hole. I have water proofed the new wall and now the big question. Should I cap this or just fill it? My worry is that water may get trapped in this area and cause me more problems later. If I cap it I would need to fill it with something in order to pour the cap. Someone suggested I build a roof for it. Any suggestions would be greatly appreciated. In the end I will be building a deck over it if that makes any difference. That may be as late as next year.

stoop

Depends which wall you waterproofed. If you waterproofed all around what was the stoop foundation, and did a good job of it, how likely is water to get trapped inside it? In that case, I would fillit with crushed stone, and then pour a concrete cap.

If you waterproofed the main foundation , and not the stoop foundation, then I would knock the top off the stoop foundation, and poke a few holes in the stoop foundation walls, and then just fill it.