You'll need:
ethyl alcohol
dish liquid
water
a big measuring jug big enough to contain the amount you want to produce

Now let's go:

1.
First you have to calculate how much ethyl alcohol you need. For this you multiply your needed liquid volume with the decimal factor of the alcohol concentration. So for example for an amount of 3 liters and a concentration of 35% the calculation will look like this:
3l*0.33~1l

This concentration is good to provide your liquid fluid till -25°C. If a lower temperature is needed, than simply rise your concentration. You can find a solid-liquid-equilibrium here way down on the bottom of the site: http://en.wikipedia.org/wiki/Ethanol
Please be very careful while handling ethyl alcohol! It is highly flamable and can cause serious injuries and brandings!

2.
Now you fill the calculated volume of alcohol in the measuring jug first and then fill it up with water till you have the wished amount inside your jug.

3.
The last ingredient is one or two drops of dish liquid per five liters. This is to solve dirt and dead insects off your windshield. You dont want your liquid to build foam or to pollute the environment, so stay with just a few drops!

Now you can fill the liquid in the tank of your car.
Normal liquid in stores costs about €5. The costs of your own liquid should be around €1-€2 for the alcohol. The rest you'll find in your kitchen.

<p>Dish liquid will strip the wax off your car. Not sure about the alcohol.</p>
<p>In the cited concentration (1-2 drops/5 litres), it is unlikely that the dish washing liquid would be able to remove much wax. </p><p>I say, Go Ahead!</p>