Choose a room in your home. A good room to use would be one that is small and compact, such as a closet or small bedroom.
Take Styrofoam insulation and nail sheets of it to the walls, doors, ceiling and floor. Make sure you leave space for the door to open and close.
Lay a thin layer of carpeting on top of the Styrofoam insulation. Use a hammer and nails to secure the carpet over the Styrofoam.
Take some empty egg cartons and use scissors to cut each one in half. Completely cover the room, except for the floor, in egg cartons. Fasten them in place with nails.
Record some vocals in your new soundproof booth to test it out. Have a friend stand outside the booth to listen for sound leaks. If they can hear any sound then you need to check for gaps in the soundproofing and add insulation accordingly.