Question
i have these RC cars that cost alot of money and no where to drive them so me and my friends are going to build a track in my back yard. i need to get rid of the lawn asap so i can get some dirt. its a huge area and have no money. i need a homemade recipe on how to kill the laawn in the fastest way possible.

Answer
Piece of cake.  Mow as low as possible (pull if necessary).  Then cover the plot with anything you can get your hands on.  Water well, then cover -- usual MO is to use Black sheets of plastic (as in Hefty Garbage Bags) , but anything opaque you put down will do the trick.  Lack of Sun is all you have to do.  Watering keeps the metabolism going -- sometimes reducing the Water kicks in a semidormant state and then it takes longer to wipe them out.  My painter removed all the Porch furniture this Summer for a week to paint, and when he lifted everything up to put it back, the Grass was dead underneath.  Housekeeper threw a party a few years ago and moved the picnic table to the middle of the Lawn on the side; when the party was over it took her a week to move it back and by then the Grass was history.

To keep the site free from Growth, you have a few choices.

One is to rake well once a week.  This slices over all seedlings and keeps them from ever getting a foot in the door.  This is also very cheap although you do have to invest a few bucks on a rake -- not a big investment here since everybody with a house that's moving this month wants to unload their garden stuff and leave the garage clean (check Craiglist in your neighborhood).

This system works better than any high priced Chemicals you pick up.  And it won't poison anyone who happens to fall onto the ground and get dirty.  RoundUp gets on your Shoes, your Clothes, your Skin -- then it gets in your house, on your furniture, into the air you breathe and then it's there forever.  Who needs that headache?  And it's expensive.  Do the old fashioned Black Plastic trick and your problem is solved.

Good luck.  Let me know how it goes.