how do build my own pressure washer with gas motor?
If you have no idea, you should probably buy one. It will be safer for you and your neighbors. :) Alternatively, take a small engine (large weedwacker etc) mount it to a custom steel frame, connect a water pump (from a car will do) to the output shaft on the motor. On the inlet side of the pump connect your fluid reservoir. Make sure your container will hold enough for the job you wish to do. Also make sure the reservoir is vented to prevent vacuum. On the output side of the pump attach the high pressure hose and nozzle. Obviously, you will require clamps, welding equipment, vibration dampening, and other fittings to assemble the contraption. You should also consider adding a safety relief valve or a bypass on the high pressure side. Speed of motor and aperture of nozzle will determine pressure of spray.