I want to length the pipe that's for the gas dryer. We need to relocate the dryer on the otherside of the washer, about 4 feet is needed. what would I be looking to purchase or get. Thank you.

The best answer I can give you for this is to ask at your local appliance store or a store that sells appliances. They are the most qualified to advise you. You will want to make sure the material you purchase allows for proper venting, as a buildup of dryer lint can sometimes cause a fire.