Determine the shape, depth, location and details of the pool design. Decide whether it will be finished with plaster and tile or a more durable custom vinyl pool liner. Obtain building permits from the local township. Stake out the perimeter, adding 12 inches to the desired size to allow for the width of the concrete block.
Cross-measure corner to corner to insure the rectangle is true. Hire a tractor operator to excavate, using a string level on the ground to verify the final perimeter is level. If the pool is to be 3-feet deep at the shallow end, dig an extra 6 inches for a poured concrete base and another 5 inches to factor in a flagstone coping and water line. Along the edge of the entire base, dig out a 16-inch wide by 8-inch deep footing.
Dig a hole for the main drain at the deep end with a trench through the wall to the pump and lay gravel in the channel after the pipes are installed. Install any necessary light boxes and wiring and make a 12-by-12-inch grid of #3 rebar at the base of the pool. Bend the bars upward along the sides of the base so the concrete block may be interlocked with it.
Have a truck pour concrete into the base as it is vibrated. Treat the surface with a rough-broom finish if you will be applying a plaster coating. When cured, after three days, begin laying the block wall to the level where the coping begins, 2 inches below grade. Cut out holes in the block for the return plumbing lines, light boxes and skimmers.
Make small, box forms for the skimmers and so the concrete will anchor them in place. Insert rebars into each of the block wall cavities. They should be long enough so that they stick up above the wall and fill each block opening with concrete as you shake the rebar and help the concrete to settle. Also pour a concrete collar around the pool walls to give them stability and add any stair details as necessary.
Fill in the outside of the pool walls with earth after the concrete has dried. Apply a plaster finish to the inside of the pool or a vinyl liner. Then set a flagstone coping along the top of the wall, using either cement or a more durable synthetic adhesive.