Chooser a room. Build the soundproof booth in confined space such as a closet, bedroom, or garage.
Nail Styrofoam insulation to the walls, floor and ceiling of the room. Don't cover doorknobs and light fixtures, however. Make sure that the insulation does not hinder doors.
Attach a layer of carpeting over the insulation. Lay the pile side face down against the insulation. Nail the carpeting to the insulation.
Empty dozens of egg cartons and cut them in half to provide a third layer of soundproofing. Take the halves of the cartons that held the eggs and attach them to walls and the ceiling. The exact number of cartons you'll need will depend on the size of the room, but for a closet-sized booth that measures roughly seven feet wide and 10 feet deep, you'd need about seven dozen carton halves to completely cover the room.
Test your soundproofing. Record audio or other noise. Have someone stand outside the booth listen. If they hear noise, check your work to ensure no gaps exist in the layers of soundproofing. Place all pieces of insulation flush.