Chloral Hydrate which is used in creating knock out drops (also known as the date rape drug) is now illegal to be in possession of without a doctors prescription. It is not recommended to attempt to make any illegal drugs. You can find more information here: http://en.wikipedia.org/wiki/Chloral_hydrate#Legal_status
Knockout drops, homemade or not, are made with chloral hydrate. They are put into a drink to make the other person, drinking it, pass out. This could be highly dangerous if you use an incorrect amount as body weight plays a role on dosage.