Unfortunately, I don't know what pool equipment manufacturers/distributors are available in Nigeria. Can you provide more details? The two most common in the US are Pentair and Hayward. Assuming your pool is rectangular, you have about 20,000 gallons (US) or 90,000 liters. Some suggestions would be a 1.5HP pump with a pool that size, one or two skimmers, 2" plumbing pipes and a 30"-36" sand filter. Of course, there are many other possibilities, depending on availability if equipment, etc in your area. Ask plenty of questions - that can usually tell if your builder is being straight with you althoigh I wouldn't automaticall suspect he isn't. Get lots of references for him.