Find the area directly behind the shower by having a helper tap on the shower wall at the faucet area. Listen to the tapping until the exact area behind the shower faucet is located.
Cut a horizontal line 3 feet up from the floor and 16 inches wide through the sheet rock or drywall, using the drywall saw. Measure up 4 feet and make another 16-inch-wide line. Cut vertical lines between the horizontal lines, creating a rectangle 16 inches by 4 feet. Loosen the nails with the hammer and remove the wall section.
Look into the opening and study the exposed pipes. Find the mixing valve, an elongated metal piece that has two pipes connected into it from the bottom and a half-inch vertical pipe coming out the middle of the top. Identify the type of material used for the vertical pipe coming out of the middle of the mixing valve as copper -- shiny metal with gray solder around the joints -- or white plastic.
Drill a hole through the wall in the shower at each spot chosen for the multiple shower heads using the drill and the 5/8-inch drill bit. Go into the adjacent room and look into the opening for the holes. Find the hole's relationship to the vertical pipe coming out of the middle of the mixing valve.
Mark a short piece of pipe with the permanent marker long enough to reach the vertical pipe when placed in one of the holes. Place the tubing cutter on the pipe where the roller touches the mark to be cut. Rotate the cutter around and around the pipe while slowly tightening the knob on its end until the pipe is cut. Place a tee on one end and a shower head fitting on the other without glue..
Repeat the same process for each hole. Do not cut off the main water line because the pipe above the mixing valve is not under pressure. Cut the vertical pipe 2 inches above the mixing valve with the tubing cutter, if it is a copper pipe.
Cut the same vertical copper pipe 2 inches below the existing shower head and remove it. Place a compression copper-to-plastic adapter fitting on each end of the pipes. Cut a plastic pipe to fit between the two adapters and temporarily put it in place.
"Dry" fit all the pipes and fittings together, placing the tees on the vertical pipe by cutting it to fit and adjusting the short pipes shower head fittings to just reach the holes in the wall. Check that all fittings and measurements are correct. Disassemble each piece individually and glue them back together using plastic pipe primer.and glue.