You can purchase concrete leveling compounds at home improvement retailers to level out the floor.
How to level concrete slab against a wall.
Neglecting to prepare the old surface will prevent the new concrete from adhering correctly resulting in a weak bond between the two layers.
Uneven exterior concrete slabs should be repaired for reasons of both convenience and safety.
An exterior wall must be placed on the outside edge of the slab so the exterior siding laps down and over the edge of the slab.
Pour and level the concrete.
Consider a wood shed floor treated lumber joists and plywood.
Drag a straight 2x4 screed board across the top of the concrete forms to level the concrete.
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.
Exterior wall on slab must be out on the edge.
Make multiple passes if needed to create a flat evenly filled area.
Add all of the concrete right away so none of the mixture has a chance to dry out.
Pour concrete onto the existing slab until it is around where you want the final level to be.
Make sure you have enough concrete to fill the entire area to the depth you desire.
You can level an existing concrete floor with a leveling layer of new concrete but you must prepare the old concrete floor first.
Have a helper add or remove concrete in front of the screed as you pull it.