One of the most popular videos on China's YouTube page is a short informative video made by Liu Xinying, showing off the "iPad 3" he made himself out of nothing but spare parts and a lot of hard work. While it may run Windows and not be compatible with the iOS suite of software (not to mention being excluded from the Apple App Store) it cost him much less than a real iPod would, and offers more power, speed and processing than any of the authentic iPads he could have purchased. Many like minded IT whizz kids have followed in his footsteps, building their own iPads not out of a desire to sell them as counterfeit knockoffs (as some less reputable manufacturers have been known to do) but instead to get all the benefits of Apple's efficient look and design without the costs and burdens associated with Apple's product.
Building a tablet PC is surprisingly simple, although it will take time, effort and a high degree of technological proficiency. The first step is to decide how much power and processing you want, what sort of battery or AC system you would like to use, and what sort of size you would like to have for the unit. Bigger units are easier to work on, but harder to carry around. Smaller units will tend to be less powerful and more expensive. In any event, you will want to plan ahead and decide what you want, and study accordingly. Below is the original video by Liu Xinying building the iPad3. You can search it on YouTube too for translated versions.
All tablet PCs are built around the screen, so your first task will be to find a touch-sensitive screen with the appropriate size and weight. Fortunately, Hewlett Packard, Dell and Sony experimented with touchscreens from 2006 until 2008, and so high-quality used screens are readily available on the used market. Many of these screens will require a stylus, and if that is an issue for you, make sure that you purchase one which is compatible with your fingers. A touchpad needs to be particularly sensitive to work with fingers instead of a stylus, and such screens will be more complex and expensive.
Next you will need to decide what you want to do about a motherboard. Fortunately, the abundance of "flat" PCs, started by the Macbook Air, means that ready-built motherboards that minimize power consumption and space are readily available. You may want to borrow the battery and solid-state memory from the laptop as well, since this will ensure compatibility and low power drain.
Lastly you will need to put it all in a case. If your touchscreen and the laptop you salvaged from are almost the same size, you may be able to simply connect the screen to the laptop with a band of hot plastic (after connecting all the electronics inside, of course) to avoid the need for a custom case. Otherwise you will need to make or manufacture a case for yourself. It is a good idea to start out with the case from either the laptop or the touchpad and then add or subtract from it as necessary.