Make sure you have enough concrete to fill the entire area to the depth you desire.
How to level concrete slab against a wall.
You can purchase concrete leveling compounds at home improvement retailers to level out the floor.
Pour concrete onto the existing slab until it is around where you want the final level to be.
Neglecting to prepare the old surface will prevent the new concrete from adhering correctly resulting in a weak bond between the two layers.
Drag a straight 2x4 screed board across the top of the concrete forms to level the concrete.
Make multiple passes if needed to create a flat evenly filled area.
Exterior wall on slab must be out on the edge.
Uneven exterior concrete slabs should be repaired for reasons of both convenience and safety.
Whether you want to refinish an uneven basement floor or replace or add new flooring on top of an existing concrete floor somewhere in your home you most likely will need to level the concrete floor.
You can level an existing concrete floor with a leveling layer of new concrete but you must prepare the old concrete floor first.
Over time concrete floors can settle unevenly or become uneven due to cracking and moisture.
Have a helper add or remove concrete in front of the screed as you pull it.
Add all of the concrete right away so none of the mixture has a chance to dry out.
This prevents water from leaking under the bottom of the wall to the inside of the building.
Consider a wood shed floor treated lumber joists and plywood.