*This is based on a 5th gen hatch.
You will need:
Plywood 48"x48", 1/4" will work well; $8.00
Sticky stuff, 3M High strength 90 works well, since its a flat surface; $8.00
Carpet, Something thin and inexpensive; see http://www.mcminone.com p/n 60-8901 for gray. Other colors are available; $25.00 for enough to do 5 of these
Staple gun and staples
Saw
Duct Tape
Scissors
Step 1: Take your existing carpet off your seats and lay it on top of the wood. I put a few staples in the carpet to hold it still. Be carefull not to break the little fasteners when removing the existing carpet from the seats.Step 2: Outline your carpet with a pencil/pen. I indented a little on the sides to allow for a slight rise in the floor in the hatch. (See the final pics below)
Step 3: Go back out to your car and measure from the base of your seats in the upright position to the base of the back of the hatch. This will be the length of your new floor.Step 4: Apply the measurement to the pattern you drew on the wood. Your measuremnet should have been about 27" for a 5th gen hatch.
Step 5: Cut it out. You will notice that the new floor wont fit in your hatch because the tabs on the side are too wide. Measure in about 7" from each side and cut the tabs off. Keep them as youll be making hinges for them, so they can fold into place in the next step.
Step 6: Using duct tape, butt the side tabs up against the main flooring and tape them in place. Dont be shy with the tape. Put it flat accross the top, then fold over the tab and put some on the bottom. (See pic)
Step 7: Now the floor is ready to be covered. Cut an ample peice of carpet out and lay it shiney side up. Spray the adhesive evenly over the carpet. Do the same on the peice of wood. Place the wood on the carpet and press down, adhering them together.Step 8: Pull the edges of the carpet over the new floor and secure with a staple on the bottom of the wood. Continue this around the border of the floor.
Step 9: Check to make sure that the tabs still are able to fold over.
Step 10: Install in your car. Install the OE carpet to the seats. Cut the excess OE capet off at the base of the seats, leaving a few extra inches to tuck down in the floor.
This is one of the more usefull things I have done to my car. I can put heavy stuff in the cargo area that would just fall through the floor previously. Its sturdy enough to support about anything. For those of you who are worried about weight, the new floor weighs 4 or 5pnds more than the stock floor. Not a big deal in my opinion.
thats what i did this summer...gonna still touch it up once it gets nice out again...maybe a little vinyl wrap or something havent decided...the one posted looks tite tho 
