Determine the type of sump pit liner which will work best for your situation. If you are primarily collecting sub-surface water seepage, a manufactured liner would be best. If working in a basement area with a concrete floor your best option will be a concrete liner which you can make yourself once the sump pit is dug. A concrete pit liner will be sturdy, long lasting and will provide a solid base for your sump pump operation.
Smooth the edges and sides of the pit, clearing away any debris or obstructions. The base needs to be level and the walls square prior to beginning the framework. A completed sump pit should be a minimum of 18 inches across and 24 inches deep. Allowing for the concrete, this means the pit opening needs to be a minimum of 24 inches across and 27 inches deep. Many pits are made slightly deeper depending on the pump style and the volume of water to be pumped.
Build a wooden frame which will sit inside the sump pit. The frame should allow for three inches of concrete on all sides and should be three inches shorter than the pit itself. Around the top outside edge of the frame install 1 inch by 1 inch boards. This will form a small seat in the concrete on which a pit cover can be placed.Take careful measurements to be certain the frame is exact in size, then set it aside until needed.
Mix the cement in the wheelbarrow, keeping the mixture slightly thick in consistency. Pour enough concrete into the pit to cover the base to a depth of 3 inches. Carefully smooth and level the base to ensure the pump will have a proper platform. Once the base is in place, carefully set the frame into the pit, atop the wet concrete. The top of the frame should be level with the floor. Check the frame to be certain it is level before pouring concrete around the form. Fill the area until it is level with the floor. Smooth and level the wet concrete to form a surface which is even with the existing floor.
Allow the concrete to set for a minimum of 24 hours. When it has hardened, remove the wood frame, being careful not to chip or damage the fresh concrete. The sump pit is now ready to have the sump pump and drain lines installed.