The wrist roller is the easiest, most effective exercise for building forearms. You can buy a wrist roller or you can go to a hardware supplier, pick up some cheap materials and build your own. If you have the money for a high quality made wrist roller, I would highly recommend it but if you are living on a limited budget then the home made version is for you. All you will need is a few cheap materials to complete your wrist roller build:

? 30″ PVC pipe with a diameter of your choice ( I would go with 2″ though)
? 5′ strap or rope

That is all you need to get started! After you pick up your materials, take a drill and drill a hole using a 5/8″ bit to allow for your strap or rope to fit through. Push the strap/rope through the hole and tie a large stopper type knot that will keep the material from slipping out through the hole ( the knot I used is called a figure 8 and it has held great for a good amount of time over a year). Now that you have your rope attached, you can now use this implement free standing or you can offset the hole you drill to allow for it to be placed on the end of an Olympic bar placed at shoulder height. By doing so, you relieve a lot of stress that can be placed on the shoulder and increase the weight being used; by overloading the movement you can in fact see huge changes in forearm strength and size.

Not really keen on carrying around a wrist roller? Well you can still reap the benefits of a wrist roller by simply looping a large jump stretch band (or any other brand) around a dumbbell and then over the end of an Olympic bar. Now simply pull the rear piece of band as you begin to roll so it is overlapped by the front piece of the band.

These two options are simple but they are all you really need in order to pack serious muscle on your forearms. As far as forearm building routines, the forearms react to lots of stimulation, so feel free to start conservatively but then gradually ramp up the volume on forearm wrist roller work in order to blow your forearms up like hot air balloons.

MORE INFORMATION: The author is an expert on lower arm training and has hundreds of articles on how to build forearm size. In conjunction with this his grip strength website will also show you how to increase hand strength while also jacking up the forearms.